I have managed to defeat every safety interlock & device that I have ever needed to.
I doubt very much that a safety interlock exists commercially that I can't defeat.
The "tool" thing is a bit, of a red herring.
A coin is not a tool.
A Torx key, is a tool
A tamper proof Torx key is a more secure tool.
Now if you are in an office environment where you have a machine used by users who are not "engineeringly" skilled, then simple hex head screws, slotted, pozi & philips would defeat their attempts to remove them at a basic level.
If you are in engineering, say an automotive manufacturing plant, they will have almost all kinds of driver bit on site, they will probably use a lot of them on their production lines.
So, how far do you go, you can get bespoke fasteners made which have unique heads, and, you can patent the tool to remove them.
Great, now the interlock is securely fixed.
I bet I can still remove it & defeat it.
Your next issue, is as safetydude1 has said, you have to provide any special tools with the machine.
So if you affix the interlocks with patented fasteners, you have to provide the tool to remove the fasteners with the machine, & make if commercially available.
Unless you can PROVE that it is not safe for ANYONE to remove the fastener, good luck with that.
You just need to apply common sense, and good sound engineering practice, then ensure that you have good procedures in place to reinforce this.
If anyone wants to take me up on the defeating interlocks challenge, then I’ll do it for free if I can’t, if I can, then you have to pay up in full.
(As per all the best adverts, terms & conditions apply!) ;)