Changing ins/outs to accomodate HW without changing global settings

I plan to add signal processing hardware (i.e., Summing mixer) to my system. I researched how to configure the ins and outs to accommodate this, but am concerned that if I do something wrong I wont be able to return to the stable system I presently enjoy. If I change the audio ins and outs, is that a global setting or will these changes stay limited to the project that I changed them in? For example if I create a template, and make these changes, will my other projects be affected?