Look no further than to the format command:
{call format ["%1_Licence_Vehicle_Car=false", _x]} forEach ["p1","p2","p3","p4","p5","c1","c2","c3","c4","c5","c6","c7","c8","c9","c10"]
or
{call format ["%1_Licence_Vehicle_Car=false", _x]} forEach _Players
A variation is to do
{call format ["p%1_License_Vehicle_Car=false", _x]} forEach [1,2,3,4,5]
{call format ["c%1_License_Vehicle_Car=false", _x]} forEach [1,2,3,4,5,6,7,8,9,10]