It is possible to move an world into an mystcraft age, I've tried it and it works. Found it on a web page, just can't seem to find it right now :-/
And it's not necessary to reset an world , I am going to do it the easy way, just make an mining age. Only time I reset the world is when the configs are altered.
So back to the moving part.... Let's see if I can remeber how I did it.
You'll need NBT explorer program (I used it)
Step 1: with the help of NBT program, open the level.dat in your world save. Expand the data node.
Write down the SpawnX,SpawnY,SpawnZ coordinates.
Step 2: Open the data folder in your world save (where you have your mystcraft ages) Open the agedata_<number>.dat (the one you want to export the world into) with the NBT software.
Step 3: Find the SpawnX, SpawnZ, SpawnY entries, and type in the numbers you have written down earlier.
Step 4: Hit da save button.
Step 5: From the world save folder ( the world your are going to copy), copy the region and data folder ( I just copied all of it) into the mystcraft age you have desided for.
Step 6: start the client/server...if on a server... log on and jump to your new age :-D
Just a few notes, I did this and it worked. just a few small bugs. Like world gen.
Hope this helpes. I know it's a bit bad explenation and my english is not the best.
Cya around .. sincerly Woodopriest