I adjusted the length of the straps of the tefillin shel rosh by adjusting the knot. I began doing this process, opening and tightening the knot multiple times as I was lengthening the straps to the correct size, but I did not say “lshem kdushas tefillin”. As I was part way through fully adjusting it to the correct length (I had only partially lengthened the straps by that point) I realised I hadn’t said this. I then said “l”shem kdushas Tefillin” and finalised the adjustment of the length, making it the correct length and making the final tightening of the knot. Have I done anything wrong here? Does the knot need to be fully untied and re-tied from scratch? I know there are serious halachic concerns when colouring the tefillin, that it must be done lishmah, but what about in this case of adjusting the knot and if I made a final tightening which is definitely lishmah was there any issue?

ב"ה Shalom, Your were indeed supposed to say " lshem kdushat tefillin”. See משנה ברורה סי' לב ס"ק רל"ב However, even though it was not said, since you had in mind to say it , what you did is fine. See שבט הלוי ח"ז סי' ז, והליכות שלמה פ"ד סעי' לא, פסקי תשובות סי' ל"ב הערה 578 . All the best