Can you dye over semi dye?

yes, but semi-permanent colors will not lift you natural hair color, and if it you put a lighter color over a darker color it will not do much other than give shine

Yes!! It might damage your hair a little bit, depending on how thin your hair is etc, but I have done this several times, and my hair is fine, just make sure it's not too soon after you died it last...

you can only dye them darker than the color there dyed, color will not remove color.

Yes but it will only take effect on the roots, and it will wash out.

Yes, You Can. But Within A Months Time. Otherwise Your Hair Will Start To Fall Out.