My vote is by way of Seasonal vendor rank resets, but the big thing with double perks when there are 2 damage dealing perks are the pre-damage perk swaps are a huge DPS advantage.
For most perks swapping off the perk automatically disables its effects but most mag overflowing or inventory boosting perks retain the added ammo which makes swapping (in edge transit's case) to Cascade Point from Envious Assassin before damage basically a weapon with 3 DPS boosting perks.
Dual damage perk options are rare, but more than that they're not limited time, and Edge Transit is currently the best GL in the game. If we're keeping this aspect of how perks work when swapped then that power shouldn't just be limited time, only the aesthetic glows should be.
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No. A shiny is a SHINY because of the multi perks. That's the whole point of it. GM weapons don't get even get dbl perks in the 4th, and you want to be able to pull them straight from the vendor for a year. Also, that proc you're talking about isn't possible without automation, not for practical use case. In game loadouts don't swap weapon perks, so it requires a DiM swap, macro, or script. The last 2 are against ToS.