No, they have a chance to be removed. When you're affixing you can see the success rates on the window before confirming affix attempt. Upslotting reduces the success rate. It doesn't do anything to the abilities themselves. If you succeed, you will have all your 5slot affixes + the one you added. IF you fail you might end up with 5 slots but one was replaced with what your were trying to add as a 6th or worse, downlsotted.
Oh dear lord. lucky my item is a mid level item lol