All I can tell you after all my trevails in this department is that
on my particular car, a 440 '68 GTX...
I've run it with heater hoses on and with the hoses removed, the nipples removed and plugs installed
in the pump housing and saw zero difference in operating temps.
(My heater box is in desperate need of a rebuid - the flapper doors are rusted and off their mounts).
I had settled into a pattern of draining the cooling system and removing said hoses every spring.
However, I installed a NAPA issue generic heater control valve (cable operated) last fall, hoping I wouldn't
have to do that whole messy draining and yanking thing again this year - and hoping to still refrain from
having "heat soak" in the interior of the car in summer. It's bad enough with headers and 3" %$#@$% exhaust
under there as it is...
We're just now entering the hotter days of the year. Jury is still out on whether the valve will be enough.
Long-winded way of answering
@Nick ciavarino 's original question - no, will not change operating temps.