It would probably be OK, but if you go up in amps like that, I recommend you do NOT get a slo-blo fuse. Because it's rated at higher amperage, it'll blow later than the original fuse anyway, and you don't want the new .25 fuse to be "still holding on" while something inside your organ fries.
If there's something wrong in the organ that is popping fuses, a .25 NON slo-blo should be fine.
But, of course, it sure would be better to get a .2 anyway... better to be safe than sorry.