OK, you can use a diplexer to run the existing CATV and your FTA setup into the house.
Find the entrance of your cable going into the house, you will then need 2 diplexers to separate and/or combine the CATV and satellite signals at either end.
1st, the outside end, diplexer #1 accepts the satellite input and then the CATV input and the combined output of the diplexer goes into the house.
2nd, once in the house, you will need to use a 2nd diplexer to separate the 2 signals to whichever TV/computer you will need them. Sat. output goes to your LNB in of the receiver, and the TV output goes to your cable tuner/box and or RF pass through port of your satellite box.