Let me answer this in stages
1)I have put in the beds 50 mm of homemade compost.I see no problem with that, but timing can have an effect
2) a good sprinkling of chicken pelletsI never put fertilisers on until I am ready to plant out, otherwise the fertiliser may have leached away before the plant needs them!
Added to which some additives e.g. Lime can react with fresh manure
3)100mm of guinee pig bedding turned that all in to the existing soil. I would have put this with the homemade compost!
4)then topped them off today with 30 mm of spent mushroom compostThis is one of those compost/manures you have to be quite careful with as this often has high quantities of lime in it and as I mentioned above this can react with manure.
Usually I was selective which beds I would use it on e.g I would use it where I planned on planting Brassicas but never where I was planting Potatoes
5)I’m hoping that should sort them out, but can you over manure and cause more harm than good?Personally I don't think so, however I think when you apply it/them can make a big difference!
This link and its relative links might help you!
https://www.thegardenersalmanac.co.uk/Content/S/Soil-Preparation/Soil%20Cultivation.htmclick on images to enlarge