Yeah, this is Darebee. You can pretty much do what you like. Sticking to programmes and such will get you the best results, but swapping a day here or there, doubling up or missing a day, it's all very forgivable - and I don't mean by us, but by your body. Currently I'd adapting the leg day of PPL, but I'm still working on completing the programme, and still thinking that I'm doing the programme. Small changes are inevitable because things happen - or you're feeling particularly frisky one day. Just enjoy it; don't stress about it. That's no fun.