Ok, I was reading Cas' epic theory response on modes and what chords to use with them, so if I have a hypothetical progression of Cmaj7 Esus9 and Fmaj7#11, when the chords change after "x" bars do I change what mode i'm playing or not?

So if I'm starting a solo in Ionian over maj7 chord, do I change from ionian to the phrygian when the sus9 hits or stay in Ionian?

It would be called Esus2. I think you meant Esusb9, as Esus2 contains an F# which messes everything up (theory wise). I'll assume you meant Esusb9.

To answer your question, no. You would play C Ionian the entire time.
or you can play the mode of the chord number youre playing
you can play the phyrgian and then lydian over Fmaj7#11
they're really all the same but the note you start on
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^That is what's going on, but your ear will naturally gravitate towards the E and F notes. Thinking about the modes changing is just confusing. Unless you plan on playing modes that do not come from the C major scale (E Phrygian Dominant works fine over Esusb9), then you don't need to think about it.
side question that relates to this thread.... Allthough they are "the same", it's the intervalls that makes them different? When you choose to play certain notes?
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Quote by backtothe70s
When you choose to play certain notes?
When they sound good.

In more detail, the progression dictates the mode. For instance, the TS's progression resolves to C, so the mode must be C major. However, another progression, Am F G, contains the same notes, but it resolves to A, so the A Aeolian mode would be used rather than the C Ionian mode.