changing int to long - does it definitely require a reindex?

[Ty <ty...@gmail.com>]

I messed up.  In my 50+ million document index, I have a field in my
schema.xml that is of type "int".  I should have made it a long; documents
that have a field that overflows that integer aren't being indexed.

Does changing this field type absolutely, positively require a re-index?
 What would happen if I simply changed the data type without re-indexing
old documents?

Thanks,
Ty