Yes, you can create a license that says that. No, you shouldn’t do it.

First, what’s the point? If you’re trying to get attribution for your work, there are a number of licenses that already require that. Creative Commons has a number of licenses that should fit the bill.

Requiring a link-back is dubious at best. There’s no guarantee you’ll get any extra traffic, and how would you enforce that sort of a request? More importantly, why would you impose an annoying restriction upon the future users of your product? You’re just scaring them away.

Trying to game search engines with a link back is also a dubious endeavor. Just because you think the engines work a particular way now doesn’t mean that they will continue to work that way in the future. My third point below really focuses on this aspect. Search engines are amongst the most rapidly changing technologies.

Second, why are you even considering changing the license structure at a later point in time? Again, what’s your point? Pick the license or licenses that meets / meet your aims and stick with it. Changing the license structure is a great way to annoy and scare off your existing user base as well as scaring away future users. The future users will say “he did this once, what’s to keep him from doing it again?”

Changing a license may mean nothing to you, but for organizations using your product it means more work. The new license has to be reviewed; it may not mesh with their legal requirements; it may force them to pick a new product to provide the same function. Don’t do it unless you really have to.

Moving to a dual license structure later on doesn’t bypass any of that additional work that you’re creating for your users as you don’t necessarily know which categories they’re going to fall into. *They* have the potential liability, so *they* are the ones who have to perform the review.

You mentioned selective enforcement of the license in one of your comments, and you might be considering that as a way of avoiding some of the problems brought up by this second point. However, selective enforcement is tantamount to discrimination. In some jurisdictions it will be tolerated, but in other jurisdictions you’ll lose all rights to enforcement. If you put a non-enforcement clause in writing then you’re merely compounding the issue by creating confusion about what the terms of the license truly are.

Third, your suggested phrasing of the change is brittle. Specifying a technology or implementation in something that it supposed to outlast various technologies is a bad idea. How would people comply in the future if the requirement is technically infeasible? The answer is they won’t and that means they won’t use your product either.

If you want to gain traction with your product manipulating the license (or search engines) is not the way to do it. The best way to gain traction is to simply write a great product. Make it available; show how great it is; keep the support active; and it will grow.

If you’re worried about a competitor copying your source then don’t release the source. Ever. License and Copyright only protect you if you can prove that those aspects were violated. Proving the violation can be amazingly difficult to do. All of the machinations you’ve suggested merely make it harder for legitimate users to use your product and do very little to keep future competitors from stealing your product. By definition, criminals don’t obey the law.