You shouldn’t be going into your stores though, you’ll be using the circulating stuff from the pre-race food.
I don’t think many if any sub-elites, are glycogen limited in any sort of long event, we’re simply not burning enough kj per hour compared to what can be consumed - the elite athlete won’t be able to eat much more than me, but will be able to burn way more than me.
It could have an impact at some durations I’m sure - but much nearer 2 hours than 10 hours - but for longer stuff is it worth the discomfort and sluggishness of feeling heavy, and is it worth the difficulty of doing the loading without the bloating of having to eat all the food.
If you do do it, adding creatine as well is probably worth it I believe.