In my experience, this may not work because the Item Object’s link to the Item registry will get stale and will stop reflecting updates to the states.
@Tommas84, I agree with HomeAutomation. What it appears you are trying to do is not possible. Your goal should not be to “simplify the reuse of [your] code in different “rules” files.” Your goal should be to avoid repeating code anywhere.
There are lots of ways to do this (note these are intended to be use in combination):