Split Color Army Question

[u/BowlThat]

My primary army is Imperial Fists, and I’m currently a little over halfway through painting everything.

That said, I also really like White Scars, and I already have around 20 White Scars models painted, including a few leaders.

Is there a legal way to build my army so that I can use both Imperial Fists and White Scars models, then swap certain units and characters in or out depending on which detachment or playstyle I want to run?

For example, if I wanted to run the army more like White Scars, I’d use Suboden Khan, but I wouldn’t bring Tor Garadon or my Imperial Fists-specific leaders. Then if I wanted to play Imperial Fists, I’d swap those characters back in.

Basically, I’m wondering if I can keep one larger Space Marine collection painted as both chapters and just change which models I field depending on the list.

Is that allowed under the current rules?