I wouldn't - ericaceous compost is for acid-loving plants. If I were you, I would stick to ordinary multi-purpose.

Manufacturers of ericaceous compost rarely put the actual ph of their compost on the bag, and they're all different. Both geraniums and petunias prefer a soil slightly on the acidic side, but your ericaceous may be a little to acid for them, hard to say until you see the results. Better to stick to multi purpose or a mix of the two if you're trying to use up the ericaceous compost.