Setting up a backup internet connection

[player1]

current setup
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-cable modem to router to computers

i am thinking about getting DSL as my backup connection. if i run into connection problems with my cable connection, is it as simple as switching from one network cable to another? can this be accomplished without a reboot?

also, during the installation of my dell router i recall entering my email and password associated with the cable internet connection. will this be an issue once i switch to the DSL cable?

thanks for any help,
jc