Well there are easier ways of farming mooshrooms for one... That is very possible though maybe. Mooshrooms have weird spawn behaviors, when using a NEI spawned mooshroom spawner they will only spawn on grass not mycelium, I think in mushroombiomes it might not care what block is in it's place at all for mooshroom spawning, but I can't guarantee anything. But a feeding station from railcraft would breed the mooshrooms for you, you just have to automate the wheat supply to the station, multiple stations would even breed them faster. The souls shards mod is even better if you can just straight up kill enough mooshrooms to complete tier 5 soul shard you can create a redstone controlled spawner that way (needs at least version 1.25 for it to work with passive mobs, not sure which is in the packs atm).