What I expected to happen was...:
The wolf's health should remain the same regardless of whether or not its data is modified.

What actually happened was...:
The wolf's health resets to 20 when its CustomName nbt tag is modified, regardless of the wolf's current maximum health attribute or health boost potion effect.

Steps to Reproduce:
1. Obtain a tamed wolf

2. Damage the wolf or modify its health using commands to make sure the health does change when its name is modified.

3. Use a command to modify the wolf's CustomName and watch the health reset to 20.

Link to video

https://www.youtube.com/watch?v=5ArH0W_V9zY