Yesterday, there was another thread on the matter, with a specific case (see
What can we do if a bounty manager did not pay the tokens as they promised?). An ICO called Globatalent Network stated a bounty of 1,1M$ and has had that information on it’s Bounty thread since January 2018 (and still is showing that value to date). Bounty token distribution started yesterday, and now the alleged bounty total for the campaign is of 0,1M$ (distributed in their tokens, not USD). Basically, they have cut the revenue ten fold, claiming miserably that they made a mistake and that the total of 1,1M$ was the aggregate for a set of campaigns, and not for this specific one.
So the answer to the question of whether it is possible to reduce the token allocation is a clear yes. It’s not ethical, and the ICO will suffer all the negative comments to come due to such low level actions. Not that they care really too much; most of these cases will likely have the objective of taking the money and good riddance to all, worst case being the investors who actually dipped some (crypto)cash into the ICO. This is a high risk environment, with barely any regulation nor control, in which wasting your personal time is the least that can happen …