Would any sources seem to indicate that if one states when talking to Hashem “HaShem if I ever regret any of my mitzvot, I don’t really regret them.” then any regrets he would have in the future would not take away the reward for his mitzvot?
The question reminds me of “Kol Nidrei”.
In KN, the request is to annul vows. These, say Wikipedia
are almost exclusively religious pledges of various kinds: That something will be done (or not done) or given in exchange for a prayer being answered, that something will be done (or not done) for religious purposes or to show religious devotion, that a thing will be used only for religious purposes (e.g., as a tool used only for building or repairing the Temple) and never for mundane purposes, that a thing will be given to the Temple or treated as if it were already given to the Temple, and so forth.
The Kol Nidrei declaration can invalidate only vows that one undertakes on his own volition. The invalidation of future vows takes effect only if someone makes the vow without having in mind his previous Kol Nidrei declaration. But if he makes the vow with Kol Nidrei in mind—thus being openly insincere in his vow—the vow is in full force.
So it is possible to nullify in advance promises to do something good. The question wants to nullify in advance a promise to do something bad (regret doing a mitzvah).
I could suggest that as we know that the deep-down intention of a Jew is to do good things (example from forcing a man to bring a korban, see here) a bad thought is essentially not what he desires and therefore it should be possible to annul it in advance.