At my company, all of our development (bug fixes and new features) is done on separate branches. When it's complete, we send it off to QA who tests it on that branch, and when they give us the green light, we merge it into our main branch. This could take anywhere between a day and a year.

If we try to squeeze any refactoring in on a branch, we don't know how long it will be "out" for, so it can cause many conflicts when it's merged back in.

For example, let's say I want to rename a function because the feature I'm working on is making heavy use of this function, and I found that it's name doesn't really fit its purpose (again, this is just an example). So I go around and find every usage of this function, and rename them all to its new name, and everything works perfectly, so I send it off to QA.

Meanwhile, new development is happening, and my renamed function doesn't exist on any of the branches that are being forked off main. When my issue gets merged back in, they're all going to break.

Is there any way of dealing with this?

It's not like management will ever approve a refactor-only issue so it has to be squeezed in with other work. It can't be developed directly on main because all changes have to go through QA and no one wants to be the jerk that broke main so that he could do a little bit of non-essential refactoring.