Yes, what you're hoping it should do should be correct. If you add enough dechlor for treating the full volume of tank to the 1/4 volume and then hose fill, the dechlor will continue to disburse in the full volume an treat it.
Whether it would "hurt" the filter is an interesting question. I've heard some mention of dechlor possibly slowing N-Bac (Nitrospira) development if used in concentrations above 2x recommended dosage (note, however, the mention was just slowing, not damage.) So throwing in all the conditioner to treat the full tank would mean its pretty concentrated just prior to the hose fill. Personally when I do this (which I indeed do, for my refills) I divide the conditioner dosing in half, hitting the tank with the first half at the beginning of the fill and adding the last half at the end of the fill. (So, note that the answer to your question is basically, NO, it won't hurt the filter, but if you want to be extra careful you might take steps like these for it not to be too concentrated at the early stage.)
~~waterdrop~~