You don't need permission from Prabhupada to follow God and he confirms this himself, many times. Just two eamples here in which he points out other Bona Fide messengers/avatars etc.
On Christ,
https://old.prabhupadavani.org/main/...tions/066.html
" Prabhupada: We accept him as avatara, saktyavesa-avatara, empowered incarnation of God. That we accept."
And Buddha,
https://vaniquotes.org/wiki/Appearan...%28Lectures%29
God became very much compassionate. When people were too much addicted in killing animals unnecessarily, He appeared as Lord Buddha.
Lecture on SB 6.1.40 -- Surat, December 22, 1970:
God became very much compassionate. When people were too much addicted in killing animals unnecessarily, He appeared as Lord Buddha. Sadaya-hṛdaya darśita-paśu-ghātam. Paśu-ghātam. The paśu-ghātam means they were being implicated in innumerable sinful activities by this process. Therefore God wanted to... Yadā yadā hi dharmasya glānir bhavati (BG 4.7). In the name of religion, they were killing so many animals. Therefore to stop this nonsense, he appeared. And he declined to accept the Vedic principles because there was no other way to stop. If he would have accepted Vedic principles, then these animal-killers would have shown him evidences that in the Vedas there is mention of animal-killing in the sacrifice. But he wanted to stop completely animal-killing; so therefore he adopted a new type of religion. But those who were followers of Vedic religion, they did not accept because that is not religion because it is against the Vedas. These are the principles.