It is as you say indeed possible to encrypt with private and decrypt with public, the mathematical symmetry in RSA allows just swapping e/d in the keys and then calling the encrypt/decrypt functions.

This being said, I want to emphasize that I'm not a crypto expert and cannot say for certain that this doesn't compromise security.

So, you could extend the RSA-Key class with that swapped logic, use blackmagic to swap the implementation of the loaded key, and pass it to the normal functions:

from Crypto.PublicKey.RSA import RsaKey
from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_OAEP
from Crypto.Math.Numbers import Integer

class SwappedRsaKey(RsaKey):
    def _encrypt(self, plaintext):
        # normally encrypt is p^e%n
        return int(pow(Integer(plaintext), self._d, self._n))
    def _decrypt(self, ciphertext):
        # normally decrypt is c^d%n
        return int(pow(Integer(ciphertext), self._e, self._n))

data = "I met aliens in UFO. Here is the map.".encode("utf-8")

# It's important to also use our swapped logic in encryption step, otherwise the lib would still use e&n (the private contains all 3 values).

private_key = RSA.import_key(open("mykey.pem").read())
private_key.__class__ = SwappedRsaKey
public_key = RSA.import_key(open("mykey.pub").read())
public_key.__class__ = SwappedRsaKey

cipher_priv = PKCS1_OAEP.new(private_key)
cipher_pub = PKCS1_OAEP.new(public_key)

enc_data = cipher_priv.encrypt(data)

# Decrypt again, just a showcase to prove we can get the value back
dec_data = cipher_pub.decrypt(enc_data)

print(dec_data.decode("utf-8"))

In order to make it work you need to convert key from str to tuple before decryption(ast.literal_eval function). Here is fixed code:

import Crypto
from Crypto.PublicKey import RSA
from Crypto import Random
import ast

random_generator = Random.new().read
key = RSA.generate(1024, random_generator) #generate pub and priv key

publickey = key.publickey() # pub key export for exchange

encrypted = publickey.encrypt('encrypt this message', 32)
#message to encrypt is in the above line 'encrypt this message'

print('encrypted message:', encrypted) #ciphertext
f = open ('encryption.txt', 'w')
f.write(str(encrypted)) #write ciphertext to file
f.close()

#decrypted code below

f = open('encryption.txt', 'r')
message = f.read()


decrypted = key.decrypt(ast.literal_eval(str(encrypted)))

print('decrypted', decrypted)

f = open ('encryption.txt', 'w')
f.write(str(message))
f.write(str(decrypted))
f.close()