To answer your question directly - no Project will not automatically increase John's assignment units to the task.


It sounds more like you need to vary resource's assignment units based upon the work requirements not necessarily dates. If you know you need resources at 75% for the reporting and presentation phases, assign them at 75% to those tasks. Don't worry about attempting to time-phase their availability. Assign the resources based upon the phases - not upon dates.

I hope this helps.