It may be possible... not a plastic model expert by any stretch but, depending on the type of plastic it might be possible. Astrobaby's suggestion is a good one to consider.
The headlight restorer thing might or might not work-- depends on the plastic and reason(s) for the yellowing-- surface oxidation is one thing; chemical changes throughout the material is quite another.
Since plastic payload tubes are usually quite thin, and age, generally speaking, tends to embrittle plastics considerably, it's questionable as to whether or not the tube can survive an extended polishing process using multiple steps or a complicated procedure anyway, or whether the ultimate outcome will be successful or acceptable or not anyway.
Without further information, I'd say it's an area ripe for experimentation. One would be advised to consider the consequences if the attempted restoration resulted in either 1) the breakage or destruction of the part, 2) an unacceptable outcome (which ties in with #1 obviously, but if the part just comes out irreversibly cloudy, hazy, scratched, swirled, or generally looking worse than when one started and/or 3) the restoring process does temporarily improve the appearance, but causes chemical damage or something that leads to increased fragility of the part or accelerated deterioration or destruction of the tube at some point in the "near future"...
Might be better to seek out a replacement, either to replace the original part outright, or as a possible substitute should the restoration process go badly...
Later and best of luck! OL JR
