create a unit with the WPs you need for the "new" group. In this init write
newgroup = group this; delevehicle this
so you have the new group with WPs but the unit is deleted.
when you have to split you have to execute this (in a trig for example)
[unit3, unit5, unit9] join newgroup
To activate a "new" WP you have to create a trigger type SWITCH and group it with the WP before the one you want to activate. when the trig fires the new WP will be the actual one.
Anyway, these are maybe the most called q's, so searching the forum, FAQs and tutorials will explain everything ;D
simon