May I ask if you are trying to modify it via cPanel File Manager and are presented with this error so far?
If that’s the case, I can remember this come up few times, the solution to this could be found using a search button .
I’d like to share a few posts recently about this here:
However, if you really have to do it like that, you can use the “Add Exception” for the particular Firewall Rule being triggered and shown as a Firewall Event in Cloudflare WAF (which Rule ID and Ruleset was it) and temporary or permanently (I don’t recommend it because of the security concert and possible plugin vulnerabilities in future which might expose it and allow the attacker/hacker to modify it via some compromised WP plugin!) disabling that rule.