Saving your test kit

If it's something like pH, you should be fine; I have been known to fill the tube halfway to the line and add one drop rather than fill it to the line and add two.
The place I wouldn't recommend trying this is with something like a NO2, NO3 or PO4 test, where you have to add different numbers of drops of each solution. For example, my NO3 kit calls for 5 drops each of the first and second chemical, and 3 of the third. I don't think it's worth even trying to see if there's some way you could figure out how to divide that kind of test up.

It should be fine in principle, even for NO3 and PO4 style tests, just round up. The reagents are all in excess anyway. Hmmm, my only concern would be with the reductant in the NO3 test. I don't know exactly what they use since we always use a reducing column in the lab (well, those rare few times that we do NO3 in the lab). Anyway, I think that it could work, try it out both ways and see if you get the same results.

Actually, my concern would be with KH/GH style tests which are titrations. These rely on adding a precisely known amount of reagent to a precisely known volume of sample. Although I know that test kits don't have the accuracy of analytical labs, you'd still have to be careful about how exactly you fill the tube. Maybe a small syringe with mL markings? Then you could add close to 2.5mL each time.

I'll have a look at it on Monday, pm me to remind me. I'm off to an Ultimate tourney in about an hour, so I'm a little rushed to give it the time it deserves.
cheers.