How big of a job would it be to change the panning button on the TCP and MCP to sliders on the default theme? Is it doable? Is there a tutorial about this somewhere?
It can be done, but it requires some WALTER skills (and free time).
I guess You can also do it yourself by "reverse engineering" rtconfig.txt file of theme that has sliders instead of knobs. But You will first need to read WALTER manual by WT, available here: http://forum.cockos.com/showthread.php?t=69767
Another option is waiting for merciful soul with some spare time
Yeah, got the Walter manual, but it's worst than Chinese to me; can't even find the files that are supposed to be at the indicated path. Guess they assume programing skills as a prerequisite.