How to add a custom RSA key pair to a .pem file

I created a custom RSA key pair just for test purposes in python. I want to add the private key and public key to a .pem file but I didnt find anything in my research. All i found is people generating a RSA key pair from a library. I have the e, d and n variables for the public key[e, n] and private key[d, n].

Most major crypto libraries support this, e.g. PyCryptodome (via construct() and exportKey()) or Cryptography (as described in the Numbers and Key Serialization sections), e.g.

PyCryptodome:

from Crypto.PublicKey import RSA

n = int("b83b...529b", 16)
d = int("4eea...a721", 16)
e = int("010001", 16)

privateKey = RSA.construct((n, e, d))
privateKeyPem = privateKey.exportKey(pkcs=8) # export in PKCS#8 format

publicKey = RSA.construct((n, e))
publicKeyPem = publicKey.exportKey() # export in X.509/SPKI format

print(privateKeyPem.decode('utf8'))
print(publicKeyPem.decode('utf8'))

or Cryptography:

from cryptography.hazmat.primitives.asymmetric import rsa
from cryptography.hazmat.primitives import serialization

n = int("b83b...529b", 16)
d = int("4eea...a721", 16)
e = int("010001", 16)

(q, p) = rsa.rsa_recover_prime_factors(n, e, d)
dmq1 = rsa.rsa_crt_dmq1(d, q)
dmp1 = rsa.rsa_crt_dmp1(d, p)
iqmp = rsa.rsa_crt_iqmp(p, q)

publicNumbers = rsa.RSAPublicNumbers(e, n)
privateNumbers = rsa.RSAPrivateNumbers(p, q, d, dmp1, dmq1, iqmp, publicNumbers)

privateKey = privateNumbers.private_key()
publicKey = publicNumbers.public_key()

privateKeyPem = privateKey.private_bytes(
   encoding=serialization.Encoding.PEM,
   format=serialization.PrivateFormat.PKCS8,
   encryption_algorithm=serialization.NoEncryption()
)

publicKeyPem = publicKey.public_bytes(
   encoding=serialization.Encoding.PEM,
   format=serialization.PublicFormat.SubjectPublicKeyInfo
)

print(privateKeyPem.decode('utf8'))
print(publicKeyPem.decode('utf8'))

Note that the raw key is symmetric in p and q, so swapping p and q changes the PEM or DER encoded key, but not the raw key (n, e, d).