1. How much does it affects that I perform a different training than the one on the calendar? (As long as the TSS is very similar) Sometimes is hard to perform the proper workout during a group ride for example.
Intensity and the length of time spent in specific power levels is more important than TSS. It is better to move a specific workout to another day when you know you can hit the goals. The more closley you stick to the training plan, the better it will work for you.