changing differential

Yes. But its going to take a lot of time, money, and custom fabrication. taking a FWD layout and converting to RWD. Everything is going to be actual custom fabrication, not just but it and bolt it in. So You first have to get the engine in, fabricate the mounts, drive shaft, axles, rear suspension, probably do some front end work, exhaust, probably relocate gas tank, and then some. Then you have to deal with the electronics, suspension for the new layout, and a bunch of other issues that you may not foresee.

Everything is possible if you throw enough money in it. There is a guy in LA that converted a Focus to RWD and powered it with a SVT Cobra engine. He dropped a little over $50K to have it done, but it is one of a kind.

lol!! that would be awesome!!! a lot of time and money. ive heard you can high psi a turbo on an ecotec. this would be a much beter engine to work with on a escort

Yes it is possible. the easiest route would be to use an existing rear drive power train and adapt it to work with your chassis. Indeed it would require plenty or custom fabrication and re-engineering. Not a very practical swap. I would recommend you sell the Escort and buy a rear drive car and spend your time and money souping it up instead of wasting your time merely doing the swap.