Is it possible at all to study one at a time in between getting various licences/ add-ons over a period of time.
Platinum, I think you are missing the point a little here, and the answers so far, although generally correct, aren't pointing you in the correct direction.
You must complete the study for the written exams by following an approved course, and get a signature from your course provider before you can sit the exams. You can not start the approved course until after your PPL. (There is nothing to stop you buying the material from your favourite pilot shop and studying at home, but you will then have to pay for another set of material when you start your course, and re-study the same subjects again, so I think any benefit from doing this would be minimal.)
You must then complete all the written exams (and yes, there are time constraints on this, but I don't think that's relevant to your question)
before you start either your CPL or your IR.
So, to answer your question directly - No. You can NOT study "one at a time in between getting various licences/ add-ons over a period of time".
However, you
are able to study at the same time as, before, or after your hour-building. This is about the only flexibility in the timing of the written exams with regards to their position in the modular course.
Hope that's some help.
FFF
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