I'm working an a Lu Chen and Yi Shan deck, There's only 1 symbol in the difference and some of there cards work quite well together so my question is, Can i have say a Lu Chen card in my deck or Side board while my active character is Yi Shan?. And could I switch characters when i swap cards between my deck and side board?.

you can have any character that is legal in the format you are playing in in your deck or side board and you can switch between games.