Model Substitution

[Thames]

There are a lot of factions that share ships within X-wing for example, can I use the Scum Falcon as a proxy for the resistance model?

[Dee Y]

There is an X-Wing Tournament Regulations document still in effect.  The pertinent entry reads:

"Multiple Faction Ships
All ship cards and ship bases in a player’s squad must belong to the same faction. If a player’s ship has different versions in more than one faction, the player may use any version of the miniature and dial that match the full ship name when assembling a squad. All dials must be from Second Edition. Plastic dial backs from the premium maneuver dial kit may be used."

This applies to official tournaments.  You should consult with your organizer for casual or unofficial events, as this matter is ultimately up to their discretion.

Note that if you use a cross faction dial, it must be identical.