Yes, the upgrade will require that you resend the snap.
Setup the replication using a local path for the snapshot (C:\something\). Make sure that its a folder that each subscriber has available with enough space for the snap.
After the snap is created, zip it up (its just text at this point and should compress nicly).
Upload it to a webserver that has a lot of bandwidth available (get a hosting account at GoDaddy or something if needed). Then at each site download the file and decompress it to the snapshot folder specified. Run the distribution agent on the remote machine to load the snap. (If you are using a pull subscription this will already be the default, if you are running a push subscription then stop the job on the distributor, and run the command manually on the subscriber).
I’ve used this technique to setup replication from the US to China over a T1 (1.5 Meg line). SQL Replication would have taken 44 days to get setup, this technique took less than 2. This should reduce your outage time to a few hours at most. You can test this by taking the snapshot, zipping it up and seeing how long it takes to upload then download. After it is zipped up it may be small enough that you can transfer it over the leased line.