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Magazine upgrades consist of a singular upgrade extending the mag, so the extended mag will protrude out of the grip as they do in real life.
Suppressors are attachable via a connection specific to the diameter and thread of a certain firearms barrel suppressor connection, so you can't connect a Pistol Suppressor to say a Sniper Rifle. Plus the volumes of gasses to be dissipated would be far different.
The laser sight in this case is unique to this pistol.
While adding scopes on pistols are possible in reality, they do not make sense to have them equipped in the game as fitting them requires the weapon's slide or body to be physically modified in order to be able to accommodate one. This means
replacing stock weapon components with modified weapon components along with the weapon mod itself. This goes against this mod's weapon modification paradigm of attachable/removable mod component added to weapon X with no modification to weapon required (Suppressor attachment to barrel of weapon excluded from rule)).
Consult: Thetruthaboutguns.com regarding usefulness of pistols with sights anyway.
Attachments/Mods can be attached and removed at the players discretion.
3rdPP views of the weapon retain mods attached to it (Say if you dropped it on the ground). NPC's may also be using a modified version of the weapon and their weapon will display attached mods.