It could brick your wii, but it would have nothing to do with your softmods. There is a chance of brick from 4.2 update for all wii's regardless. If you do update you'll have to softmod again.
I would imagine there is a work around. I have not played the game, so I don't understand the process, but if you use the shop channel, you don't need to update the wii for that. Just update the channel and the required ios file. This is described the guide, have a look at the two linked below.
Also I would imagine that those songs are available elsewhere.