Yes it is quite easy to switch algorithms via the "gpr" parameter. You just have to write a wrapper class. I am currently working on a repository that discusses how to do that in detail: https://github.com/SimonBlanke/surrogate-models I will upload some examples (GPy and Gpflow) within the next 24 hours.

I think those wrapper-classes will already answer some of your questions. If you have additional or unanswered questions you can open an issue in the Grad-Free-Opt repository.