where is your defaultdomains.xml file located? It could be on one of two places:
1) under Data Modeler installation - datamodeler\datamodeler\types directory.
I assume yours is there - then you can copy it to new DM's instalation
2)directory set in preferences - "Preferences>Data Modeler" - "Default system types directory"
Once that directory is set that directory will be taken when next version of DM is started and you don't have to worry about domains.
If you decide to not import preferences from previous version then you can set it manually.
In SDDM 3.3 EA2, I am still unable to reassign a data type definition for an Object Type's attribute that is defined as 'NONE' as the result of a lost domain definition file. Currently the only way I have found to fix this it drop the object type and then recreate it. But do that drops all the hooks to references object types, object tables and object / relational tables.
In SDDM 4.0 EA1, this problem is fixed. A lot of improvements between the latest version of 3.x and 4.0. The DDL generator and the way if formats as well as solving the DDL dependency problems is a huge help! The added functionality in the object model and how we can use domains for parameters and .dot notation for key generation finally provides the functionality I have been waiting for a number of years. Finally, the diagrammers and the new panel that shows the bird's eye view of where you are on the diagram was a very nice surprise and a huge help when working with large diagrams.
Thanks to you and all of the SDDM team!