For blyxa japonica, I would just pull everything up and seperate. When you pull it up, you will see several seperate crowns with its own roots. You can then either re-plant the stems or sell it in the sns. In a matter of weeks, you will probably have to thin it out again.
Yes they will grow. Viciously attack it with a razor blade, its not going to die unless you dice it to small pieces.
Don't be afraid to hack away pieces that are overgrown. Its very hard to kill aquatic plants by cutting them. Sometimes plants even sprout from pieces of leaves that float around for a few weeks, so you don't need to worry at all about how to cut it. Just chop it back so it looks good and forget about it.
thanks... that advice is true with many plants. I will give it a try with the B.j. There is that initial tendancy to not want to temporarily make the tank look bad. However, my parenting Keyhole cichlids are uprooting everything in sight as they move their brood around the tank, so i dont want to take a chance with pulling up the old plants and trimming the plants from the bottom up. Those fish wont allow them to stay down once replanted.
Will let you all know how it turns out.