Nah - cos in the second pair of lines it adds both the pollid and userid INDEXES, it needs to drop the userid index to do that INSERT in a "neat" way - the DROP in the first pair is for that reason ...
If you have applied Xenon's optimisation, then you have the pollid and userid INDEXES, in which case you need neither of these queries ...
Another way to do it would be to drop the pollid index in the first pair - to gain the "neatness" referred to earlier