Update: Using the more recently updated EE converter tools from Norbit, I was able to open (as LSX) both the player.lsb from Main.pak and the player.lsf from MainLSF.pak. Both of these files have the fields for player runspeed (default 3.75, I tried 5 and I tried 5.25 in case the decimals mattered). Converting them back and putting them into their correct subfolder still doesn't do anything. The player.lsb gives me the "main stuff is corrupt you can't do multiplayer" but no speed effect. The player.lsf does nothing either.
My guess is that the tools can't open/save the files properly (creating a bit of corruption), the game refuses to let the changes work, or I'm just not good enough to understand (probably this one). I'm writing this post in case it might help someone who's trying to work on this as well.
