iRule with regex to allow illegal URL entry on ASM as string will change everytime.

You can test your regex with something like regex101.com, so you can see that your Regex will work, but in this case this iRule has nothing to do with ASM (it is an LTM iRule). If you need to create an ASM policy to only allow URLs in this specific format you can use wildcard URL, but beware that wildcard entities in ASM do not support full Regex language and have a limited syntax (described here: https://support.f5.com/csp/article/K8623)