I came across this blog post because I’m thinking about attempting something similar very soon. I’m planning (among other mods) of switching around the A and B buttons to make Mega Man Anniversary Collection more playable. I’ll be posting and possibly a video tutorial in the next few weeks on my website http://www.frankacy.com

About your solder not wanting to stick, there could be a couple of reasons. First of all, make sure you’re using a solder with a flux core, it’ll help it stick. Also, you need to make sure that the contact point in sufficiently hot to accept the solder. Sometimes on surface-mount boards such as these, this can take a while because the heat spreads through the whole metal contact (thermodynamics) instead of just where you’re applying it. It may take a little while depending on how long/wide the trace is. Oh, and you could always use a hotter soldering iron