You can't remap the MP or MR tunes. What you see is what you get.
If you want to do a custom tune you need to buy an unlocked ap3 and start over. Probably not what you wanted to hear. Sorry about that.
Not true.
The DP isn't going to be accounted for in the MP275 tune, so you may have issues with the car running oddly. To be honest, I do not know what it may do to the car, but it usually isn't good when you have all that extra flow, but the ECU is only giving you enough fuel for the stock DP, which can cause lean conditions. In the Subaru world, this means BOOM. The Ford ECU's are pretty smart, so as long as you don't drive it hard, you should be ok until you get the tune addressed.
You would need to contact Mountune to purchase the MR300 tune. See the link below;
mountune MR300 Performance ECU Calibration
You will have to buy the better charge pipes for your intercooler likely. It doesn't need to be Mountune, but again, the MR300 kit includes the upgraded charge pipes so the tune will be set up for that.
You will be fine, you just need to spend a few more dollars, or remove the DP.
Upside is, the MR300 kit is 300chp and 350ctq