No, you won't ruin it.
However, there are some things to think about. I used the refil kits before, and they work pretty good mostly. My Cannon printer would leak the thinner ink out into a well under the print head, so I had to refill it every 2-3 weeks if I used it or not.
Make sure it says that it's compatible with an HP, you don't want it to damage the print head. If it does, a new print head comes with a new cartridge usually.
It is usually cheaper to refill them, and you won't damage anything that isn't replaceable by just buying a new cartridge.
I say try it!
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