This year I am doing a siyum on Chol hamoed. It's the fifth time I have done a siyum on Chol Hamoed .
If the outline of the remaining letters is written before Yom Tov and the siyum involves just filling in letters,it is permitted to do so on chol hamoed because such work is not considered maaseh uman. It is for this reason that it is not uncommon for a siyum to occur on chol hamoed.
My question is, if something goes wrong i.e. there is a smudge or mistake that needs to be repaired during the siyum process - and the skill needed to fix it is masseh uman - ie we are not just filling in letters anymore, this is a proper tikkun - what is the din? Thankfully it has never happened to me, but I was wondering what happens in such a case and if anyone has experience in this matter.
A gut Moed!