Codex question

Hey guys just wondering if it is possible to make a codex variant like the "Angry Marines codex" and still be possibly legal. The reason why is because as most of you know I bought a Valkyrie a week ago and have no plans right now to make an IG army but I do want to have a chance to actually use it in a game. So while I was at the store today I overheard some people talking how you could almost mix the armies up, like have any of the Imperium forces use any of the other (imperium forces) stuff like the valkyrie or a leman russ. That got me thinking about a combination of Imperium forces, like it's space marines meets IG. Maybe I'm just going out on a lost cause but it just kind of had me wondering.

if you been reading up on diff codexes you later find out that Ig and Daemonhunter can be taken as buddy units( i forget the name) along with space marines. Have u ever seen grey knight with Imperial gaurd same differece. the valkyrie is and good question on if should/ can be taken with space marines, ill go ahead an research for yah. So endign on a lighter note * you can take the units but it won't effect the rest of your army except that unit.

Alright makes sense now. Thanks Angello.

its called allies I believe, in the alinment codexes the talk about an chart whit numbers of units and what kind of units you are aloud to take