Enforcement on ill sub that becomes ill part

[ljudge]

I was brushing up on rule 9 this morning, specifically illegal participation. If B has 10 men on the field and a sub runs on to the field as the ball is about to become live and doesn't get onside I know it's illegal substitution simultaneous w/ the snap. If he participates or influences in the play it becomes(?) IP. Does the illegal sub BECOME illegal participation, or is it technically a multiple foul situation? I'm assuming it's a multiple foul and if the IP is enforced the enforcement spot depends on whether it was during loose ball play, running, play, etc. vs. simply a previous spot enforcement as you would have if you only had an illegal sub.

In other words I'm thinking the IP doesn't "count" as simultaneous with the snap. Is my logic correct?