Change filter in assembly mode from geometry to part as the default

In an Assembly, If you go to File - options - selections and move Part over to MyFilter, then click the box below Set My Filter as the default selection filter, I *THINK* you will get what you want...I haven't used this much so I don't know how it really affects other areas.

Another option, make a mapkey to change the selection filter.

Honestly, I stopped changing the filter for much, I realized that even if I selected a surface of the part, if I RMB it would give me the options as if I selected the part. I do still use the filter a lot in large assembly drawings, saves a bunch of selection delay time.

In order to expedite selection workflows, we have defined macros to set the selection filter on the fly. If you use mapkeys to do this, you may need to ensure they are built such that they work across all modes (i.e. part, assembly) when invoked. You can add a macro to the UI if you want to invoke it using the mouse instead of the keyboard.