I celebrate this feast as per the following proper, which some might find useful. I found it in an early version of the Anglican Missal.

January 30th.
CHARLES I OF ENGLAND, K. & M.

Introit. Domine in virtute tua. Ps. 21.
The King shall rejoice in thy strength, Lord, exceeding glad shall he be of thy salvation : thou hast given him his heart’s desire. Ps. ibid. For thou shalt prevent him with the blessings of goodness, and shalt set a crown of pure gold upon his head. V. Glory be.

Collect.
Blessed Lord, in whose sight the death of thy saints is precious : we magnify thy Name for thine abundant grace bestowed upon our martyred Sovereign ; by which he was enabled so cheerfully to follow the steps of his blessed Master and Saviour, in a constant meek suffering of all barbarous indignities, and at last resisting unto blood ; and even then, according to the same pattern, praying for his murderers. Let his memory, O Lord, be ever blessed among us ; that we may follow the example of his courage and constancy, his meekness and patience, and great charity. And grant, that this our land may be freed from the vengeance of his righteous blood, and thy mercy glorified in the forgiveness of our sins : and all for Jesus Christ his sake, our only Mediator and Advocate. Who liveth.

The Lesson from the former Epistle of blessed Peter the Apostle. 1 St. Peter 2. 13.
Dearly beloved : Submit yourselves to every ordinance of man for the Lord’s sake : whether it be to the king, as supreme ; or unto governors, as unto them that are sent by him, for the punishment of evil doers, and for the praise of them that do well. For so is the will of God, that with well-doing ye may put to silence the ignorance of foolish men : as free, and not using your liberty for a cloke of maliciousness, but as the servants of God. Honour all men : Love the brotherhood : Fear God : Honour the king. Servants, be subject to your masters with all fear, not only to the good and gentle, but also to the froward. For this is thankworthy, if a man for conscience toward God endure grief, suffering wrongfully. For what glory is it, if when ye be buffeted for your faults ye shall take it patiently ? but if when ye do well, and suffer for it, ye take it patiently ; this is acceptable with God. For even hereunto were ye called : because Christ also suffered for us, leaving us an example, that ye should follow his steps ; who did no sin, neither was guile found in his mouth.

Gradual. Ps. 112. Blessed is the man that feareth the Lord : he hath great delight in his commandments, V. His seed shall be mighty upon earth : the generation of the faithful shall be blessed.

Alleluia, alleluia. V. Ps. 21. Thou shalt set, O Lord, a crown of pure gold upon his head. Alleluia.

After Septuagesima (omitting Alleluia, and the verse following) is said :

Tract. Ibid. Thou hast given him his heart’s desire : and hast not denied him the request of his lips. V. For thou shalt prevent him with the blessings of goodness, V. Thou shalt set a crown of pure gold upon his head.

+ The Continuation of the Holy Gospel according to Matthew. St. Matt. 21. 33.
At that time : Jesus spake this parable unto the multitude of the Jews, and the chief priests : There was a certain householder which planted a vineyard, and hedged it round about, and digged a wine-press in it, and built a tower, and let it out to husbandmen, and went into a far country. And when the time of the fruit drew near, he sent his servants to the husbandmen, that they might receive the fruits of it. And the husbandmen took his servants, and beat one, and killed another, and stoned another. Again he sent other servants, more than the first : and they did unto them likewise. But last of all he sent unto them his son, saying : They will reverence my son. But when the husbandmen saw the son, they said among themselves : This is the heir, come, let us kill him, and let us seize on his inheritance. And they caught him, and cast him out of the vineyard, and slew him. When the Lord therefore of the vine yard cometh, what will he do unto those husband men ? They say unto him : He will miserably destroy those wicked men, and will let out his vineyard unto other husbandmen, which shall render him the fruits in their seasons. Creed.

Offertory. St. Matt. 7. 12. Whatsoever ye would that men should do unto you, even so do unto them : for this is the law and the prophets.

Secret.
O Lord, our heavenly Father, who didst not punish us as our sins have deserved, but hast in the midst of judgment remembered mercy : we acknowledge it thine especial favour, that, though for our many and great provocations thou didst suffer thine Anointed blessed King Charles the First [as on this day] to fall into the hands of violent and blood-thirsty men, and barbarously to be murdered by them : yet thou didst not leave us for ever, as sheep without a shepherd, but by thy gracious providence didst miraculously preserve the undoubted heir of his crowns, our then gracious Sovereign King Charles the Second, from his bloody enemies, hiding him under the shadow of thy wings, until their tyranny was overpast ; and didst bring him back in thy good appointed time to sit upon the throne of his father, and together with the Royal Family didst restore to us our ancient Government in Church and State. For these thy great and unspeakable mercies we render to thee our most humble and unfeigned thanks ; beseeching thee, still to continue thy gracious protection over the whole Royal Family, and to grant to our gracious Sovereign King N. a long and a happy reign over us : so that we that are thy people will give thee thanks for ever, and will alway be shewing forth thy praise from generation to generation. Through Jesus Christ our Lord and Saviour ; our only Mediator and Advocate.

Communion. St. Matt. 16. If any man will come after me, let him deny himself, and take up his cross, and follow me.

Post-communion.
O Lord, we offer unto thee all praise and thanks for the glory of thy grace that shined forth in thine Anointed, our Sovereign King Charles: and we beseech thee to give us all grace by a careful studious imitation of this thy blessed Saint and Martyr, and all other thy Saints and Martyrs that have gone before us ; that we may be made worthy to receive benefit by their prayers, which they, in communion with the Church Catholic, offer up unto thee for that part of it here militant. Through.