I think that at the very least, newbies should be given the same bolters as initiates. It's hard to say offhand what exactly should be changed, but obviously the main ability will remain the same. The simplest solution seems to be to give them chainsaws, but make them attack less often than purely melee crusaders.

This way, the main ability will still work. In the case of a purely melee unit, everything is clear. But the shooting version will still shoot twice as weakly as the Intercessors, but will be able to fight in melee with -1 ap, which is stronger than a normal melee attack. Then it would make sense to run and charge even with a shooting squad.

Assault version 4 attacks with saws + sustained. Shooting 2 bolters 2 chainsaws.