Hi Lennart,
I have been looking if it was possible, but it's a Source template and it says:
Source templates for formatting, e.g. Template:EE_citation, are not recommended. New templates for source formatting should not be created and existing ones should not be added to new profiles. Ideally, the existing ones would be removed from where they have been used in the past, but this is not a priority.
Source templates for using the same source on multiple profiles — what could be called "source shortcut templates", e.g. Template:DGFA-1 — are not officially recommended but they are not officially recommended against. Continuing to use them is not a violation of the style guide, but they should be used with great care. It is possible that they will be officially recommended against in the future, or officially recommended.
So I can ask if it's ok but looking at what it says, I think the answer will be no and because it's possible these templates are going to be removed from all profiles again in future, I don't think it's wise to create one ..the Findagrave one is also a Source template...
I think we can wait a bit and see what's decided about the Findagrave one, found this G2G where it says Findagrave is more an external link template and that perhaps it will approved...