Are the "Maximum Armor Modifications", Arsenal p44 a required thing?
I've used them for so long in non-SRM games I had forgotten they were actually an optional rule.

Tweaking Armor Encumbrance, Maximum Armor Modifications, Armor Suit Capacity, and Armor Degradation are all optional rules. The Shadowrun Missions campaign does not use optional rules.

And ummm... Arsenal has only been out for a couple months...

I think what is being asked is,

Well in the core book on page 317 it talks about armor Modification, and as far as teh book states there is no limit so technicly you could have a armored jacket with lvl 6 nonconductivity,fire resistance,thermal damping ect, not counting the effects on things like drones, so with arsenal being out are the rules on page 317 of SR4 still valid? This would be important since at least for me in normal games I have armor mods on my lower level armors and things like leather jackets, lined coats ect,

That's correct. And, Arsenal adds even more options that you can pile on to a single piece of armor. Wasabi was asking if we were using the Arsenal rule that limited the number of those modifications. As that's an optional rule, we're not using it for Shadowrun Missions.