Relinquishing and reissuing stock - no 83(b) election

I just wanted to post this question to see if anyone has dealt with this before. A founder received restricted stock (not options) in 2024 and no 83(b) election was filed and these shares vest over a number of yrs. Now a 409a valuation is being done as an equity plan is being developed with ISOs etc. Since the founder has a taxable event through his block of shares, is it possible for him to relinquish his shares and reissue to himself? And can this be done before the new valuation from the 409a study so as to still lock in his original low valuation?