Operating under the assumption that there are no intervening factors i.e. mandatory crossing altitudes etc then my question would be...why would you want to start a descent to 2500ft? Given your scenario I am assuming that you are established on the LOC and you are currently below the glideslope. I think it better practice to maintain 4000, intercept the GS and then down you go in one continuous stabilized descent to the runway. I am not sure why you would want to descend to 2500…intercept the GS and then start your descent again. However the answer to your query is that given the scenario described then yes you technically could start your descent to 2500 providing as you say that you meet any and all restrictions detailed on the plate.