Is there a way to include OpenID as a drop down option in the contribution lis? or Is there a way to convert OpenID to external identifier?
a) Is there a way to include OpenID as a drop down option in the contribution list? 

If you created a custom data field called "OpenID", you need to make sure the field can be used for contributions and that it is marked as searchable for it to appear in the list of fields when mapping contributions for import, 

BUT

if memory serves me correctly, the system will require either an internal or external contact ID when importing contributions, so...

b) Is there a way to convert OpenID to external identifier?

Since you already imported the contacts, you can export all contacts being sure to include the OpenID and internal contact ID fields, then the update can be done in one of three ways - which ever you find easiest:


Use the import contacts wizard to update all contacts mapping the OpenID to the external contact ID field using the internal ID as the link, OR
Use a vlookup in csv to match the internal contact ID to the OpenID in your contribution data import file, and then import your contributions based on the internal contact ID, OR
Use an SQL statement that will copy the OpenID to the external contact ID field by contact ID directly in the database


Hope this helps,
Tamar