I have experimented top dressing many different amendments in - EWC/compost, lime, epsoma products, and guanos.
And yes you can... It is best to mix in the amendments/fertilizers into the top few inches of the soil, and not let it sit on top, otherwise they will get moldy with watering.
A point to remember is with any organic based fertilizer, it is essentially slow release. It has within it some soluble fertilizer, with the rest again slow release, and the fertilizer release rate has numerous factors... This is where you will incur variability, especially and particularly with granulated or slow release fertilizers that have not been specially formulated for cannabis (which I am sure will come to market soon).
You can add too much of any organic fertilizer if over applied.
Guanos will be "hotter" in this regard so be careful not to overapply, the fertilizer within should last a given amount of time. (so for you liquidcooled420 that's a good rate you started out on and I'd almost cut back half that dose, or wait a little more time before dosing again, unless you start to notice a deficiency, there should be a decent amount of elements in that amount of fertilizer plus you are applying every week, that could start to accumulate if over done. I know I've done that which is only why I'm cautioning it, but it was 1.5 gal pots not 5 gals so you may be okay with that feed rate and their needs, but you're also gonna need potash in there.. I donno what guano it is, I think epsoma's guano is 10-1-1 and has ca and mg and other traces in it.. hm.. i should check the bag..)
EWC is about the only thing you really can't overdo. Well, you can, but like, lol at that point dude you don't need that much ewc. whos wastes worm gold? For realz. That shit is gold lol.
You're still always going to need a PK booster, and during the right time during flowering... I hear, and I have found myself, that many in organics will get "airy" buds, even with good lighting, and this is the PK boost that needs to be applied at the proper time. Low levels of K throughout may also be warrented, and some Ca at certain points (and mg), is also going to be needed in soils as plants uptake elements from the media. Nearing the timing of a PK boost and to flush carbohydrates can be added to aid microbial activity, which can be added with EWC tea. (though soil doesn't get "flushed", it's just using h2o with nothing really added at the end.. well, depending lol.. I don't wanna get too deep, with say, using yucca and h2o with your flush, and yadda.. heh, or, heh, you could use ewc tea up to like the last week or so..)
EWC/EWC tea adds a host of things that are in any of those given bottled nutrients - some nitrogen and micro nutrients, microbes, chelating agents, etc., If plants are going bad, ewc is really good. Teas and EWC can be overdone, it's hard to do it, but you can. The only place ewc isn't warranted is in real hydro setups with regimented fertilizer schedules, rockwool, and stuff like that. Dirt or most coco setups can use ewc just fine. Theres plenty of better info around of course than I could give on the subject. Or any of these topics lol...