50% het, means there is a 50% chance it is het for that gene. It either is, or it isn't, there is no middle ground, but until you breed it you dont know. The same principle applies to 66% hets, they just have a little better odds. So once babies come out, you'll know if the parent "proves out" and is in fact het hypo, or if you lost the coin flip and it isn't het hypo. So assuming your mark. leucistic is in fact a visual hypo, one of two things will happen with this pairing. Either: 1. half the babies will come out hypo, and the other half het hypo, meaning your 50% het hypo 50% het trans adult can then forever be refered to as het hypo 50% het trans. OR, 2. A bunch of normals hatch out. which are all het for hypo from the hypo/m.leucistic parent. This will mean that you lost the coin flip with the 50% hypo breeder, and it is not het hypo in any way. You'll then simply refer to the 50% het hypo 50% het trans, as only 50% het trans without mentioning hypo in any way.
The 50% trans part works the same way, but sense the other adult isn't likely het trans, you wont learn anything in that regard from this pairing. If it is in fact het trans, half the babies will be het trans (a bunch more 50% het trans), but your not going to know if they even have that 50 50 shot sense you wont know if the parent is even het. Basically, you gotta beat the coin flip on the parent before you even know if the babies get a coin flip on the het trans part.