A few years ago when it seemed like the wild west compared to now, you could do nearly anything and get paid.
So subs would learn they could make some extra money and start doing fence gates without pools. However, HUD regs dont state anything about it and the nationals got charged back for this. And they in turn charged back the vendors (thats me). Not all were chargebacked. I think I got something like 40 chargebacks in 2010.
The short answer, no, dont do it unless you specifically get approval.
Having said that, we have good success bidding to put padlocks on electrical panels (prevents someone turning the power off, stealing things etc).