[Exim] forcing a 451 error on purpose in exim 3.35.

In exim 3.35, is there a way to force a 451
based off of an expansion string result condition?

For example:

-> MAIL FROM: <sender@???>
<- 250 2.1.0 Sender ok
-> RCPT TO: <recipient@???>
<- 451 4.7.1 Please try again later

I would like to send a 'yes' / 'no' (boolean)
to a "defer_delivery" type configuration,

so as a made up example:

defer_delivery = ${perl{subroutine}}

### in exim4 I think it would be something like:
### acl_check_rcpt
###    require domains = +your_domains
###          condition = ${perl{subroutine}}