Is it OK to change the direction or the height of a rigid copper pipe by bending a long run slightly? I am not talking about heating the pipe and bending it to change its shape, just pushing the pipe "a bit" to get what I want. Or does this put undue stress on the pipe and solder joints?

For example, when plumbing a long run under the floor, I'd use different height blocking to bend the pipe to a new height as an alternative to adding in two fittings (two 45s or two 90s) to change the height.

For another example, I want to move my shower head by about 2 inches left. Could I just open the wall, push the valve assembly to the new position I want, and secure the valve in that new position? How much can I bend the pipe under stress and leave in that position of stress before I am asking for trouble?

On a side note, someone advised me I could put a "kick" in the pipe by using an inline coupling and just soldering the two pipes into the union at the angle I'd need thus getting all the direction change I need right there. How much angle change could I get or is this also a bad idea? In this case I am wondering about the solder filling the join uniformly all the way around.

I'm in California, btw, but guessing code and practice on this is pretty much the same everywhere.

It is fine, BUT, extremely "ghetto".

Why not just use 1 or 2 more fittings and a little more copper and make it look good?

why not install a section of soft copper

Copper fittings have a fairly "snug" insertion so the amount of "flex" is very limited. Once the joint is made, you can "move" the copper as needed, although it violates most good workmanship standards, as long as you do not "kink" it.