Alan - to get back to your question, in the past I have practised tonglen and metta in addition to AYP. Here's some advice, for what it's worth
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Get really stable in your AYP practices first. Then you can try adding/changing things. What I did was alternate metta (in the morning) with samyama (in the evening). I never included tonglen within AYP, but as it's the ultimate 'portable' practice, I simply fitted it in during the day.
I'm not a Buddhist, and I have heard varying opinions about doing tonglen - the general opinion seems to be that it's a good idea to be familiar with metta practice first, then add tonglen later, however, I learned tonglen first (a teacher I respect and have done a lot of work with suggested it to me, and I liked it from day 1) and later added metta - and apparently this isn't that unusual.
As Yogani says, the guru is in you - and you'll find your own way - but I'd suggest you get your core AYP routine firmly in place first before you start fine-tuning, adding or substituting. That way, you have a baseline to refer to, in terms of effects, so that if overloads start occurring you know why and what to do to smooth things out. This is just my two cents, and feel free to ignore
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