Better-Engineering Label

What does this label mean for issues on the github repo?

Hi,

We use it for improvement that are not new features but would be nice to have from an engineering point of view: it makes the code easier to read/easier to extend.

Is the contribution process any different for these? Should I open an issue with design details?

If it is just a simple cleanup, you can send a PR.
But if you have any doubt, do open an issue to discuss this!