Suppose I'm a particle. Do I come along and say, "How do I feel like behaving at the moment? Shall I do the quantum trick or the relativity trick, exercising choice so as to make my behaviour unpredictable by any conceivable physical law even of a probabilisitic nature?" Or in fact is the way I behave completely described by some physical law(s)?

It seems likely to me that particles behave in accordance with physical laws which completely describe their behaviour, probabilitically as appropriate, in any circumstances. Whether we are capable of discovering/describing them is a separate matter.

Your apples and oranges didn't make much sense to me. Two "different" laws are actually two parts of the same law provided that there is a link between them saying when each applies in a complete and consistent manner.