It depends on what the consequences are if the relay fails. For example, what happens if the electrical contacts overheat and start a fire or weld together so the current does not shut off when you want it to? You will probably be ok because most electrical components are designed with a substantial safety margin HOWEVER they design and rate devices for specific applications for good reasons. As soon as you go outside of what it was designed for, unless you happen to be a real expert, you are using up some unknown portion of that safety margin. If you are going to put the project together, run it for a few minutes or hours while you are standing there running it and then dissassemble it so no one else will ever use it, probably low risk. If the worse thing that could happen is that you burn up a $100 motor or kill yourself, that is one thing, if it fails and could kill an innocent bystander or a bus load of school kids, that is another.