I am not sure what you mean. When you try to open a Generic model, you have the option to open an Instance also.
You cannot open the Instance by itself and then open the Generic. It has to go from Generic to Instance.
The Generic is the first model that all other Instances are based on. If you want to see the Instance names in the OPEN FILE window, then change the config.pro setting "instance_search_exhaustive" to
"yes", ("no" is default).
Specifies the extent of an instance search. You must specify the type of Pro/ENGINEER file when you enter the instance name, either by typing it in the input panel, or by selecting the type in the drop-down list in File > Open.
yes-Searches for instances that would be listed in an instance index file, if one existed. The search may take some time, especially if some of the search-path directories are on network servers. If the specified instance is at the end of the search path - or does not exist at all, the entire search may take a very long time and you may get the erroneous impression that there has been a system failure.
no-Retrieves only instances that have previously been regenerated and that would be listed in an instance index file, if one existed. Checks every generic model in the current working directory, and then in every location along specified search paths in order to find and retrieve the particular instance.
If no .idx files are present, Pro/ENGINEER looks only in the current working directory for instances. It will not look in each generic model found in the search paths.
Steve