Does that actually work? Is it enforceable? I would imagine that if you sent back a contract with modifications for their review that they would balk at hiring or you would get involved with the lawyers who are so much better at legal negotiating than you are.
I definitely would not do that with a consulting contract. The chance that something weird would come up is generally worth it to get a good client.
Yes, it's legal and enforceable. Your signature is on the contract that you sign, not on some mythical un-marked-up copy.
In fact, this is often a good negotiating tactic: someone hands you a contract, and they just want to get it signed.
You strike out the price and write in a new price (or whatever), initial it, sign it, and hand it back.
The psychic weight is now on them - they have a SIGNED CONTRACT and all they need to do is to sign it themselves.
Taking the conceptual step backwards from a contract (albeit only signed by one party) to a contract signed by NEITHER party is a bit hard to do.
IANAL, but if you cross something out of a contract, sign it, and the counterparty also signs the contract, then the part you struck out is not part of the contract. The trick is getting the other person who's signing the contract to sign it even though you've crossed things out.
In my experience, people and organizations often purposely make their contracts over-reaching just to be on the safe side, and expect savvy customers/partners to cross those overreaching items off.
I definitely would not do that with a consulting contract. The chance that something weird would come up is generally worth it to get a good client.