What does the DomainSpecifierRegExp do in ManagementModule.xml (located in the module JAR file)?
Is it still utilized?
If so, if we specified a domain found in domains.xml for this property would it automatically filter agents in this domain?

Release:
Component: APMISP

It is not used for the purpose of filtering agents in a domain. I
If we create a Management Module under super domain and also create a Management Module under a custom domain.
The entry, 
<DomainSpecifierRegExp>(.*)</DomainSpecifierRegExp> 
is the same in both ManagementModule.xml 
We do not suggest to modify this parameter in ManagementModule.xml