Hi femotvaff,
I know I repeat myself, when I'm writing: The rDNS - entry has to be made on the nameserver of the provider. It is not possible to change IP based rDNS - entries on your rented server itself. Even if you would create a PTR entry over your own nameserver, this doesn't result to a propper reverse to your rented IP.
Let's assume you rent a server at BEST-ROOT-SERVER-OF-THE-WORLD-AND-AS-WELL-ON-THE-NET.ORG, they might assign a static IP ( or more ) to your rented server, for example:
IP: 999.999.999.999
Domain: server999-femotvaff.BEST-ROOT-SERVER-OF-THE-WORLD-AND-AS-WELL-ON-THE-NET.ORG
The IP 999.999.999.999 comes over the IP-Pool assigned to BEST-ROOT-SERVER-OF-THE-WORLD-AND-AS-WELL-ON-THE-NET.ORG and so BEST-ROOT-SERVER-OF-THE-WORLD-AND-AS-WELL-ON-THE-NET.ORG has their own nameservers, where they create rDNS - entries for their customers as stated in my example.
Let's assume further more, that with your root - server, you have as well 1 domain included from BEST-ROOT-SERVER-OF-THE-WORLD-AND-AS-WELL-ON-THE-NET.ORG ( in this example it is : femotvaff-buisiness.org ), but you didn't ask your provider to reverse your server IP to your including domain and so the reverse entry still points to server999-femotvaff.BEST-ROOT-SERVER-OF-THE-WORLD-AND-AS-WELL-ON-THE-NET.ORG. "Nice" provider grant access to their nameservers, where you might modify the reverse entry from server999-femotvaff.BEST-ROOT-SERVER-OF-THE-WORLD-AND-AS-WELL-ON-THE-NET.ORG to your included domain femotvaff-buisiness.org, but deny entries from external domain - provider ( in this example EURODNS ) and only let the customer change reverse DNS entries to domains, which the customer got over BEST-ROOT-SERVER-OF-THE-WORLD-AND-AS-WELL-ON-THE-NET.ORG, or charge the customer for external domain entries on a monthly basis.
You certainly may assign as many domains as you would like to over EURODNS to your server - IP, but the reverse DNS entry for a IP from the IP-Pool of BEST-ROOT-SERVER-OF-THE-WORLD-AND-AS-WELL-ON-THE-NET.ORG, will still be done over the nameservers of BEST-ROOT-SERVER-OF-THE-WORLD-AND-AS-WELL-ON-THE-NET.ORG.