Depending on how close the two project templates resemble eachother, you should be able to replace by index number from one to the other.
If that fails, best bet is to:
1. purge all unused attributes
2. duplicate the existing english attributes to a new attribute with a very high index number
3. delete and replace each original english attribute with the new english duplicate attribute
4. you should now have a project where you can use attribute manager to add all the spanish attributes without overwriting any existing attributes
5. delete and replace the high index english attributes with the preferred spanish attribute
Depending on how many things are used, this shouldn't take too long.
Just mind that there are some more things like renovation filters, graphic overrides etc that will be english, so in the end you might also want to merge the 'Spanish'-fied 3D model into a proper Spanish new empty project.
Good luck!
Erwin Edel, Project Lead, Leloup Architecten
www.leloup.nlArchiCAD 9-26NED FULL
Windows 10 Pro
Adobe Design Premium CS5