So , my question is the following , can i have two abilities from the end of skill tree and change from the one to the other one occasionally ?
Yes, you can 
So, i can have the hacker ability and the one that you deploy ticks ? Without bugging something .
One at a time - yes.
you could for example have the one that lets you loot ticks, and the one that gives you a free respawn - then during combat, use the free respawn one and when you are done swap to the one that lets you loot ticks before looting any robot corpses
Do you know if it aslo works with the one that lets you hack robots and the one with the ticks ? (they are both in tech skill tree ) .