Mix is no different than other blends ...
All mix is hotter than light mix hence the nitrogen excess. With a soil like this you can make it less hot by cutting it with a mild potting mix or bottom fill for later super soil like use.
Adding kelp would be fine as would EWC and bump in myco . The EASIEST method of FEEDING would be a top dress with same soil as needed over time. Soil is already precharged , young plants may suffer a little until they become acclimated to it. Same issue with FFOF fox farm ocean forest blend.