Hi, you can try to split it and make something like below:
sometext._domainkey IN TXT ("v=DKIM1; k=rsa; -p=first 200 chars"
sometext._domainkey IN TXT "last 200 chars")
or one more way:
sometext._domainkey IN TXT ("v=DKIM1; k=rsa; 200 chars" "last 200 chars")