Well, this puts us squarely in the realm of "If a tree falls in the forest and no one is there to hear it, does it make a sound?" My understanding was that any change in the past creates a divergent timeline, no matter how insignificant or noticeable the change is. If Cap went back in time and fought beside original Cap in WWII, that would for sure be a divergent timeline. The fact that he hides away in a house relatively unnoticed by anyone but Peggy shouldn't impact the laws of time, space, or alternate dimensions. That should still create a divergent reality. And yes, if he lives in the divergent reality, then uses the suit to get back to the original dimension he left, then he should by all rights appear in the same place he left, just like baby Ant-Man, right? Or are the Avengers we see at the end of the movie actually in a divergent reality?
There is a culling of the divergent realities in the comics, where a chain reaction starts causing divergent realities to "collide." I didn't follow it very closely, but I believe its an incursion centered around Earth. Both Earth's exist in close proximity for a short time, but if nothing is done, both Earth's and their respective universes are obliterated. However, if one of the Earth's is destroyed, that alternate universe also dies, but the surviving Earth and its universe are maintained. Well, until another incursion hits. It was really just a convenient way to start cleaning up all these abstract realities/dimensions. I think that story is too complex to do in the movie universe, but this alternate dimension/multiverse stuff opens the doorway for that kind of scenario down the road. As I mentioned previously, whatever we're seeing at any point now may not be the "core" dimension. I'm betting we get some hints at this in the new Spiderman flick.