I don't think the question is dumb.
I think you worded it a bit weird though.
Are you talking about switching from MH to HPS?
If so, it depends on what kind of ballast you have.
Most digital ballasts will run both MH, and HPS.
If you are using a ballast that will run both you would use the same fixture and ballast and only need to switch the bulb.
Peace.
Tav