> How to use GPL libraries in commercial products?
Exactly the same as any other. It's a free license, so she , by definition,
returns the right to use this work for any purpose, including commercial.
> If I ... [change] the names of functions, classes, variables, procedure declarations and implementations of functions, the order of executable code and release a library under the new license incompatible with the GNU GPLv2.0, it is technically possible to prove the violation?
> Were there any cases of bringing to responsibility for the described actions?
I do not know any. Not any nonsense, which can be described, someone actually does.