too late for mushroom compost on brassica beds?

new year's resolution of actually planning allotment rather than plonking plants in any available space is coming on nicely. except that the spot i've got in mind for brassicas is where the potatoes went last year. whereas my book says i should be planting them where I had peas and beans last year (as they were planted on a pit of kitchen compost) (and which is where I'm extending the strawb bed to instead). or alternatively that i should have dug in compost in autumn (which i intended doing, but then it rained. then snowed. then it was Christmas. then more snow.).

so -- i have 4 "spare" bags of mushroom compost. would it be ok to dig/top dress the intended brassica beds with this, on the basis I won't be planting out til late spring? or am i too late, and should just sprinkle some lime on the patch and hope for the best?

last year's potatoes in this spot had a little composting earlier in the year and were mulched regularly with grass cuttings. our soil is clay, and quite wet at the moment. (hence wanting to top dress rather than dig).