I guess you will need some more powerfull tools to redo the animations yourself.. If oinkerwinkle and notepad are your best tools, you will need to do what chilla-killa said. It's tedious in oinkerwinkle, but i've done it succesfully once (replacing the goblin in the shredder for a mortar team guy).
The trick is to use "vertex group of selection" to check what group goes where and compile a list (33 - Right shoulder, 34 - Lower back, 35 - Left Hand etc). Then you use "assign vertex group" to make the new rider behave properly by adding the right values to the proper vertices (I roughly deducted which nodes should behave as "shoulder" etc). Note that if you make a mistake or forget a node your animations will be screwed!! You can check the groups required in notepad aswell (they are the last series of numbers under geoset).
You could then try to use the animation transferer to gain more animations but i doubt there are many compatible units..
Altenatively you could use triggers to simulate the mount, but the bouncing of the wyvern will seriously screw it over. I'll place the idea anyway but i suggest you just go with oinkerwinkle.
- Make a riderless wyvern and a dummy rider with locust.
- Trigger: Move dummy to wyvern each 0.02s (and maybe change the flying height to match the wyvern)
- Trigger: A unit is attacked by wyvern -> Play dummy attack animation
You can take the full triggers from my campaign.