Those aren't equivalent, and in fact one is ungrammatical. Words like ever and any are negative polarity items in English. When the verb is already negative, you need to use an NPI not another negative.
- They will never be able to mess with him. (verb is positive, so needs a regular negative word)
- They won’t ever be able to mess with him. (verb is negative, so needs an NPI)
Here's the same sort of thing with any:
- We have no bananas. (verb is positive, so needs a regular negative word)
- We don’t have any bananas. (verb is negative, so needs an NPI)
There are lost of other like this. It’s a topic still open for research, one we still don’t know squat* about.
PS: Yes, squat is actually an NPI; follow the links — twice — for why. :-)