And I don't see this as "fly under the radar" at all. They should look at the contract they get back from you, just as you should look at the contract from them. If they don't even notice that you crossed stuff out, that's hardly your fault.
Regardless, the employer almost certainly has a very high caliber legal team, and you? do you even have a lawyer? You think that you're going to get the better end of the argument in court based on an extremely tenuous thread? That's not the smart way to bet, you're more likely to get your ass handed to you. If you want to modify your employment contract you need to be upfront about it.
I'm curious as to how this would play out in court, though. They say you agreed to such-and-such in the contract. Asked to produce the original contract, they pull out a copy with your signature and the relevant clause crossed out and initialed by you. Is the court really going to say, "Well you didn't initial it, so even though you clearly saw this change and accepted the signed contract and said nothing about it over the X years that Bob worked for you, we'll say that it's still in force"?
I'd also like to know why "they still started their employment" would be considered to be implicitly agreeing to the employer's version of the contract, while "they still paid their employee" would not be considered to be implicitly agreeing to the employee's version of the contract.
I can see how you'd get in trouble with the tactic of just taking the contract and then ignoring it. But you get a contract, you counter, everybody shakes hands, you're on the payroll and somehow that implies that you agreed to theirs, and not vice versa? How could that possibly be?
If someone can't have a conversation about an employment contract any more politely than "no verbal response" I have to wonder how they ever get hired in the first place.
The "must disclose any existing inventions or ideas to the company now and that anything not enumerated belongs to them" is what does it. Almost none of my offers have ever included such a line. Any company trying to push that does not deserve a respectful response.
I can have a conversation about the contract. But when the contract includes that, it is like being given a serious minimum wage offer.
Is there a reason why one should quit instead of negotiating the contract while also letting them know you are offended by their initial offer? (Of course, if my current employer pushed something like that on me, I would be starting to look around.)
If anything, quitting is likely worse than being let go because you likely have less of a claim with regards to unemployment (a lawyer would need to specify the actual details).