Migrating from Multi-Select List to Enumeration List

To my understanding, changing data type is not possible directly.  I had tried a lame attempt to modify the configuration source but it dint go that well though I cannot recollect what was not it exactly.

However, one possible way could be to use child project areas..

Suppose you have a Multi-Select List Process Template, create the Parent Project Area PPA_M from it
Create a replica process template
   delete the multi_select list
   add Enumeration List data typed attribute with same ID as the Multi-Select List Attribute from PPA_M
Use this to enum typed process template to create new Parent Project Area E, PPA_E

Enable Process Sharing in both the parent projects PPA_M, PPA_E.

Now any child project CPA_ChangingAttribType of PPA_M will have Multi-Select List Attribute
When you need to change the type, change parent of CPA_ChangingAttribType to PPA_E

Since the attribute id's are same, the type should most likely, effectively change.

Hope this gives the required solution or atleast some direction towards an answer.
Cautionary Note : I have not tested this for any dependencies that might be affected..