As far as I remember, you can't modify a reservation the day of, even if you call. Seems like a lot of potential trouble just to avoid a ferry (or monorail) ride.
I'd also like to see the new walkway. But, yes, avoiding public transport is what I'd like to try to do. I understand Uber is "public transport" as well, but a lesser risk I'm willing to deal with. I'm staying in the Boardwalk area so I can walk to 2 resorts. I wanted to walk to MK as well since it's a possibility.
Disney certainly allows people to come (via monorail) to any of the MK resorts to eat at restaurants and drink at bars. So I'm not sure I agree with the thought that they are trying to lessen the pandemic load on their hotels by not allowing drop off at the front door. But yes, it is what it is.
And since there is such a clear advantage to arriving before the 'sanctioned' transportation can get you there, it just makes sense to try to figure out a way to do it (IMO). We may try the walk from TTC if it's a nice day.