On 2-Aug-2005, Don Bowey wrote:

I suspect it would. In the early days of radio, filament voltage
rheostats
were sometimes used to control volume. Also as tubes aged the voltage was
cranked up to keep it usable.

Forgive me if this comment is out of place, but I think I see a trap here.
It is very easy to use the terms "heater" and "filament" interchangeably.
They are two entirely different animals and should be treated accordingly.
The comments regarding reduced life at reduced voltage would probably apply
more to indirectly heated cathodes (heaters) rather than directly heated
cathodes (filaments).