Cross Training in Marathon Taper

I am sorry if this information is given somewhere else, but I do not remember it from the documentation I read at the beginning of the training plan.

I am 2 weeks out from my marathon and have been using Level 1 (Power) to train. This plan only gives 1 week for the taper.

My legs have been feeling very fatigued for the last week and a half of running, and I wonder if I can replace one of my “Foundation Runs” during this week (2nd to last week) and one of my “Foundation Runs” next week (last week/race week) with some biking or swimming. I ask this because my legs feel tired, and I don’t know if a 1-week taper might be enough for them to feel fresh on race day. This change would obviously provide a reduced training load and maybe help me recover? This is my first marathon, so I know very little, but this is what some people recommended to me.

I appreciate all your input!