Is it Ok to reverse the usage of public key and private key
No, this doesn't generally work:


encryption / decryption could use another padding scheme if it switches depending on what kind of key is used;
if the private key is leaked / made public then the public key can usually be guessed or calculated - this works at least for RSA and IES encryption using DH keys;
the crypto library may not be able to switch around the public key and private key, for instance for RSA may require the CRT parameters and ECC keys are different altogether.


A wild guess: in 60% it would not be feasible, 35 percent it would be completely insecure, 4 percent just less secure and in 1 percent of the time hey, you could be lucky and have something that approaches secure, all depending on the protocol, algorithm and implementation.