I have a MAG 254 STB with the the original remote but I don't use MAG 254 as it becomes non responsive and needs rebooting frequently possibly due to insufficient processing power and RAM.
I now use StbEmu Pro on the Fire Stick 4K and was wondering if I could use my infomir MAG 254 remote to control StbEmu Pro on Fire Stick
No way because they both different way Mag run Infrared and firestick run Bluetooth so no way to pair but you can use Firestick remote app from your smart phone.