The claim shall prevail. Namely the technical scheme outlined in the claims.
The change also depends on the situation. If his change is still included in your claim, which brings better results, and he wants to implement the scheme that must implement your patent, then he must get your consent to implement it.
If his amendment is suspected of spying on your technology, but his plan is not included in your opinion, that is, you didn't think of such a plan at first, then he can not ask your permission, and the scope of protection of the two of you is different. Even if you say that he infringed afterwards, it is not within your scope. The law can guarantee your power, but it can't restrain the creativity of others. Therefore, if your plan is well thought out and described properly, it will be difficult for others to cross it.
Another situation is that his modification directly replaces the usual means that people in the technical field can obviously think of, such as changing the nail used for fixing into a bolt, which can be said to be infringement.