Don't have a suggestion as I'm going to hit that crossroads soon m'self with my Elec/Devices blaster.
I can answer the other question though. If you choose a power from an Ancillary power pool you won't be able to choose anything from the patrons once you unlock them, unless you use a respec (Which means you'll be able to re-choose that power at the 35 mark as a patron power).
I think the general thought though is the Defense shields in Mace Mastery and Cold Mastery serve better than the Resist shields found in all the others because it's easier to build defense with IO sets. Though not sure how easy that is for blasters
I just got my AR/devices blaster to 44 last night, and I took the munitions. Body armor with luck of the gambler ftw. The RLM is awesome, especially IO'd.
Now to answer your question. You can change over to Villian patron pools, but there is a quest to do it.
1)you'll have to jump over to villian first and this means lots of tip missions(if you're a hero).
2)Once a villian, you need to run the patron arc, which is funn on all of them, but it will take some time going through them and it being a redside arc, teaming will be hit or miss.
3)Once you have completed the arc, you will need to respec your toon and choose a patron power.
4)Thematically, its hard to add a patron to my ar/devices toon. But I chose Black Scorpion, since it comes with a mace with mace blasts, one of the best armors in Scorpions shield, on another blaster toon.
Personally if you are going thematically, go with munitons. Cryo ray, body armor, LRM. Fun powers.
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Thanks for the advice. I'm going with Munitions, since it sounds like a decent power set and it fits my theme. I have an unused respec, so it's easy to change things around later.
Rogues can get access to patron powers, right? Or do you have to be a true villain?
yes rogues get aceess
I know this reply is somewhat late, but I think you'll like munitions. It's very synergistic with the AR/DEV. Body armor is a nice addition, and does *not* have the additional graphics which drive me nuts with most shields -- plus, it's always on and doesn't detoggle. However, IIRC, you can't use LoTG in there, since it's a defense set. I ended up using pieces of the PvP Gladiator's Armor with the across the board defense unique. Works just as well in PvE, for my purposes. 
Cryo hold is my utter favorite of the set. Surveillance is not bad as a debuffing power; I just need to remember to use it. I used to use LRM much more than I do now that I have Judgement; I may, however, spec out of it and pick up another power altogether.
Hope that helps. Can't help you on which patron pool would help, although I'd think Mace Mastery would be pretty good. You wouldn't need web envelope, but the cocoon would be a hold, and I'm always in favor of pets, just, well, because.
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I just hit level 35 with my AR/Devices rogue blaster. I'm trying to decide on an epic power pool. Any advice?
The ones that tempt me most are Munitions and Flame. Munitions would fit with my character's theme (nothing supernatural) and Body Armor would be nice to have (I am squishy). The initial powers for Flame don't look that exciting, but Fire Shield looks useful, and Rise of the Phoenix is very shiny.
Also, will choosing an epic power pool now prevent me from getting a patron power pool later? It's not clear on the wiki.