Can shapefiles that I’ve uploaded be edited if the habitats are different on the ground?

Yes, this is a key process in the UKHab Survey. One of the main workflows people use is uploading shapefiles as “pre-survey” data. This is largely to provide you with the habitat features pre-mapped for groundtruthing in the field.  The main UKHab survey then uses these features as a template for you to either accept as-is or edit to reflect what you find when you survey them in the field.