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.
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.
Have you ever worked at a large company? Did this work?
I feel like at large companies, this would be like trying to modify the language of a car rental agreement, and the HR rep would just be confused.
Large company. East-coast based. Where non-competes are legal and common.
Working on the left coast, I demurred.
I got the left-coast version of the contract, no non-compete.
In other circumstances, I might request a substantial portion (up to or exceeding 100% of my salary, given that actual costs typically run 140-200% of salary) for the duration of any noncompete. Consideration.
In this particular case, when the property I was working for was divested (and riffed) some time later, I has fully unencumbered. Others had noncompetes, though these were not valid in that state. I'm not aware of any action being taken on the basis of that contract, but noncompetes can and have been enforced (notably recently between Microsoft and Google trading employees back and forth).
That said, this is precisely the sort of thing a labor union or professional guild would be in a very good position to make more acceptable standard boilerplate for.
I am not a lawyer. Suppose a rental car matter ended up court. I would rather not have to say to the judge, "I spent 10 minutes thoughtfully reading and evaluating the contract, and after careful consideration decided to accept the agreement." I would rather be able to say, "Gee, it was printed in gray ink in tiny type on the back of the paper, and they told me to just sign here on the front to get the car. I needed the car, so I did what they told me."
I never accept the "standard contract" when it comes to employment or consulting gigs - then I always read carefully, propose alterations, and often talk to my lawyer. But if it really is a "standard contract" signed by millions (including, presumably, lots of lawyers, too) then I am inclined to balance the risks and benefits and opt for ignorance over informed consent.