you can use the 'advantage pack' tools if you want to swap the model for a different model from within your idw.
if you don't have access to the subscription bonus tools then you can still do it manually simply by
1. (temporarily) changing the filename of the original model before opening the new idw (copy of your first idw), when you try to open the new idw you will be then asked to pick the iam file that you want to use since inventor will not know where the original file is anymore. after you tell the idw which model to use, the it will finish opening at which time you save your new idw (or save copy as if it is the original idw that you are opening).
don't forget to give the original model its original filename after you are done saving the new idw. usually you can use a system like the following in case you forget to fix the filename, so that otheres who may stumble accross such a filename will know that is is just a forgotten step from a previous job...
originalfilename_zzz.iam (use this to snooze out whilst swapping models as mentioned above).
2. using design assistant to replace the model in the new idw.
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