How can I check the entire hierarchy in my Regex

Summary:

I want to create a validation that checks the entire hierarchy for specific values.

For example, if a user has a request to ADD Geography H001, I want to check that there is a corresponding "admin" geo already set up anywhere in the hierarchy. All admin Geos should begin with the first 2 characters of the geography and end in 99. Thus, I want to have a validation that checks that H099 is somewhere in the structure.

The issue is that this admin geo can sit anywhere in the structure. I cant use call out Ancestors in the Regex because, as shown below H099 will not be a parent but a bottom level in a different roll up in the structure. I cant use sibling because H001 and H099 do not roll up to the same Parent. Is there a way to call out/check the entire node set in the Regex logic?