I also preach about the efficacy of using packages to organise related integrations.
e.g. all of my HCM2Payroll integrations go into the pck_hcm2payroll - you get the idea.
I then proceed to demo the creation of an integration and forget to add it to a package.
I'll have to stop doing this!
Now I can do this afterwards.
Simple example -
The above is the integration from the previous post.
I open the integration in edit mode - and click on the menu option - Primary Info -
Here I can add package details - either entering a new package or selecting an existing one.