There used to be some mechanism for importing but aside from basic stuff, there isn't, really. You will have to set up the following things using myworlds again for existing multiverse worlds:
Make sure to load the worlds again using MyWorlds. You can also opt to load both MyWorlds and Multiverse plugins at the same time. Then MyWorlds will pick up when Multiverse loads up new worlds and take over configuration options like the chunk generator plugin used.
Stuff you probably have to change after
These things you will likely have to configure after:
- Time. E.g. /mw time always 12:00 for always day
- Weather. E.g. /mw weather always clear to disable rain