Do you mean that I won't have enough computing power also later, after the staple maximizer's proposal is stated, or that there isn't enough computing power just during the thought experiment?

You will have enough computing power later.

What does it mean to self-modify if no action is being performed, that is any decision regarding that action could be computed later without any preceding precommitments?

I mean suppose Omega gives you the option (now, when you don't have enough computing power to compute the millionth digit of pi) of replacing yourself with another AI that has a different decision theory, one that would later give control of the universe to the staples maximizer. Should you take this option? If not, what decision theory would refuse it? (Again, from your current perspective, taking the option gives you 1/2 "logical" probability of 10^20 paperclips instead of 1/2 "logical" probability of 10^10 paperclips. How do you justify refusing this?)