New LED lights affect my turn signals flash

Common issue. The LED's mess up the current draw through the system. The only good solution is to switch back. One of the problems with having computer control of everything they are set up for the OEM parts only.

Will load resister on wire of headlights matter much?

It might but if you have to add resistance it may cause other issues.

I put back stock headlights. I replaced turn signal multi switch on steering wheel. I still get intermittent signal on both sides.