ICANN has said they will never delegate .internal and it should be used for these kinds of private uses.
I'm a coauthor on this Internet draft so I'm ofc rather biased.
Does reusing it cause any problem for the mDNS, or does mDNS usage cause problem for the internal-domains usage?
And then when you reconfigure it, depending on the stack it won't bother querying mDNS at all if a DNS resolver responds.