Yes, you can reload as you like. If using PEP1, you will want to go no higher than 7.1.21. Version 7.2.22 and higher are for PEP2 and forward and ProntoScripts on Firm Keys do not work if you download a PEP1 config to a remote with 7.2.22 or higher firmware.

Bootloader will never change. It is 'Application' that you are mainly concerned with.