Work allowances

Hi.
I have read that there is such a thing as a work allowance, which will not affect your LCW/ LCWRA status. Is this correct?
I am in the process of waiting for a decision on whether I will be classified as having LCW or LCWRA. I have not been able to work for 13 months and my employer is arranging a meeting to consider my dismissal.
I wonder if I agreed to work a couple of hours a week if this would or could jeopardise my case as the DWP could argue that I must be fit enough to work full time. Or would it be better if I waited for a decision on which group I'm in. I'm trying to imagine a situation where they wouldn't question your health by working. I have severe back problems