If you mean keeping the reservoir full of vegetative nutrients, and then adding flowering nutrients to it, no, don't do that. If you do decide to do that, only do it for the first week or two of flowering, when the extra nitrogen could be used for stretch.

The problem with not changing your nutrients is that you can't be sure of the composition. You can't tell how much/little of the vegetative is left in the system, to be mixed with the flowering nutrients. You are better off knowing, as exactly as you can, the composition of your nutrient solution so that you can make adjustments as needed.