Can this be applied after aggregate has been revealed before sealing?

No, QUIKRETE® Liquid Cement Color - Brown (No. 1317-01) is only designed to be used as an integral color modifier by blending with the clean mixing water before mixing in with the gray dry powder concrete mix or gray dry powder mortar mix. You may add color by staining the concrete after it has cured (minimum of 28 days) with QUIKRETE® Concrete Etching Stain (No. 7215-25 – Tan; No.7215-26 – Coffee) or QUIKRETE® Translucent Concrete Stains (No. 7215-02 – Cola; No. 7215-04 – Light Brown). Precautions will need to be taken to prevent stain from getting onto surfaces other than the concrete. We always recommend trialing small areas to experiment and evaluate the color after at least 24 hours to determine if the color on the concrete and exposed aggregate is acceptable before initiating full scale project.