Guilty! Used a ton of VNSP PAR64s back in the 80s and if I noticed sag, I would spin the sucker 180. Hard to say if it had any effect as the "longer" filament would probably just sag in the other direction, but did it anyhow! Besides, the VNSPs were very visual in that you just look in the front of the can and you don't need to disassemble or unplug anything to "spin the bottle."(I've heard of some people flipping the lamps if this is the case - YMMV)
Some things NEVER change! Way, way, WAY back when I was in High school, we had a series of instruments located in a cove. You could access them from a catwalk above the ceiling. That's where I hid the replacements lamps! Right under the catwalk, next to the fixtures.Well in my school auditorium, we wait until a lamp goes, then go to the box of a dozen spares I purchased to find it empty because another building needed them. Then I submit another requisition for 12 light bulbs (yes I know they are lamps, but if I request lamps, the purchasing agent brings in all the table lamps in basement storage and tell me to pick from them to save money). Then the purchasing agent assumes they are LED light bulbs due to the cost, and won't approve them because I just bought a dozen a couple months ago. After explaining, they research replacement LED light bulbs that they believe will work, but of course they will not, so they bid my request out to 3 different vendors, none of which can beat the price I submitted originally. Finally the Purchase Order is generated, waits to be approved by 3 administrators and submitted to fill the order. The Lamps arrive 3 days later, and I install one, and place the remainder in storage for another building...
So to answer the original question, I replace lamps about 6-8 weeks after they fail.
I assume they are not easily accessible so therefore group relamp.My main fronts are all 750w HPLs with a 300 hour life, so I pull them about 3 times a year. Generally I'll wait until one or two blow to prompt me, then I'll do the whole pipe unless it's been less than 4 months since they were last replaced. The rest of my instruments I re-lamp when they blow.
On the other hand, in some places getting access to the fixtures is a problem. For instance, most schools in my area don't have the equipment to reach their FOH positions in their gymnatorium/cafetorium/who-thought-this-was-a-good-idea-atorium. In those places, if you lose one lamp then it's best to replace all of them at the same time.