Will I be able to change my fork?
Best to stick to 26" specific forks. 27.5 forks will alter your ride handling due to the increased fork offset/rake and increased axle to crown length. 

Increased fork offset/rank will reduce the fork's stability (ex. self-centering effect). The fork offset issue is a major issue, especially for higher speed gravity-assisted riding. The steering twitchiness increases, which can lead to micro-corrections when cornering (rather than a calm smooth arc) and the wheel is more liable to deflect left/right when hitting bumps head on.

Increased axle to crown length will rotate your bike's geo back, notably increasing BB height (compromised cornering and stability), slackening the seat angle (compromised seated pedaling position). Also, the reach is shortened, stack is raised, and rear center length (horizontally chainstay measurement) is increased.

You can mitigate the axle to crown length issue by running less travel up front, but then you compromise on your travel and dynamic geometry, which includes your ride height at sag and such, which would require further fine tuning.

Note that you can still get upgrade kits and custom tuning for 26" fork chassis, if you feel that it's becoming out of date. For example, RS offers a Charger damper for 26. 

The industry has abandoned 26" for 27.5 for modern high end performance MTB designs. You will see fewer options down the line for forks, tires, and wheels. Expect production to be further discontinued, due to lack of demand; note that manufacturers of complete bikes are undoubtedly the biggest customers, not retailers and individuals in aftermarket.

I personally have a Stumpjumper FSR EVO with a 26" BOS Deville fork, and it has less significantly less breakaway resistance than a new Pike and 36. The damping is different, but I can't subjectively say if it's something I prefer or not; I just know that it hasn't let me down nor is repulsive in any way. Versus the prior CTD fork, I've been crashing far less (from often to almost never), but a bit of the bike's playful and thrilling character has been lost in the process (feels more behaved and mature).