Dont you have to lift the engine up to do that??
From what I can tell, you would need to at the very least use a hoist to take the weight off the mounts. Then you would need to get a wrench inside the mount & unbolt the mount from the tranny, take the bolt out of the mount & take the top half the mount out. This would allow access to the rubber insert. Each one would take some serious work I bet. Unless they are ripped, I wouldn't.
Nope, the mounts that use the inserts aren't weight bearing mounts. They only keep the engine from twisting forward and backward on acceleration. I've seen both of them out at the same time and the engine didn't drop down at all. In fact, it's actually suggested to unbolt both from the engine when installing a header so you can rock the engine back and forth to get more room to work with.
The front mount is a piece of cake to remove. Easier than an oil change.
Just remove the bolt up top from the engine bay, and the bottom two bolts from under the car. You don't even need to remove the engine plastics.
The rear is a PITA, though (mainly wiggling it around to put the inserts in, then wiggling it back into place), but it's the one mount that really needs the reinforcement, most likely because it's exposed to the heat of the header (which weakens it, causing it to tear).