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Would applying multiple patches to a ROM normally result in the intended effects of each patch being successfully applied?

I really have no idea how the patching process works and it occurred to me that the altered conditions of one patch might disrupt the "accuracy" of another's changes.

I've been playing through i90east's expert version 2 patched rendition of FF6 and I later stumbled across an evade bug fix that causes evade to correctly cause Evade to affect physical attack avoidance rather than MBlock. I don't know if i90east made this correction in his patch and would like to apply the change, but I don't know if it would work. The i90east patch was pretty extensive, swelling the original ROM by 1meg.

On another note, it'd be really nice if I could find a change-log for for i90east's Expert Version 2 hack but ever since he stopped frequenting forums and his website disappeared so did all information on the project.

The patching process is very simple: the IPS file lists the differences between the original ROM and the patched ROM so your patcher can make the necessary changes. It basically says, "Ok, at this place, put in a 3. Here, replace the next 5 bytes by these. Etc.. etc.."

However there's a potential problem with this. Let's take two fictional patches.

Patch A: Replace the 10th byte by "10", the 11th by "8", and the 59th by "6"
Patch B: Replace the 11th byte by "9" and the 22nd by "8"

So you apply patch A and everything's fine. But when you try to apply patch B, because it too writes something to byte 11, it ends up overwriting part of the changes patch A made. And in an extreme but fairly common case, this can be assembly code. Having a byte set to an unpredictable value in the actual code is almost certain to cause serious problems that general cause the game to crash.

So basically, try and see if you don't know for sure wether the patches are compatible or not. If the game crashes at some point, just revert to a version of the ROM with only one of the patches. If you're playing with saved states, you're extremely likely to be able to just pick off from where you last saved even if the ROM uses a different patch (unless the changes were very radical, like changes to maps or the scenario data.)

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