Updating backend used by a list file via Stats socket

Hi Everyone,

I am struggling to identify the correct syntax to route hosts defined in a list file to a different backend e.g. for temporary maintenance, via the stats socket. In the HAproxy config, I set an acl based on a string map of the list file:

acl rule1 hdr(host),map_str(/etc/haproxy/routing/listfile.lst) -m found
use_backend backend_1 if rule

I’ve looked at set acl and set map, neither of which appear to be appropriate, at least in how I have attempted to use them. I am sure there must be an easy way; can anyone pls point me in the right direction? Thanks!