The privileges of a CRI are clearly written in JAR-FCL 1.375: to instruct licence holders for the issue of a type or class rating for single pilot aeroplanes.
The licence does not have to be valid to do this; therefore, you can do any of the things a FI does except give abinitio instruction to a non licence holder. If you only hold a PPL you cannot be remunerated for it.
As a PPL with TMG rating, could I gain a CRI and then offer conversion training to PPL SEP's? Also of course revalidation flights for SLMG and TMG, which I suppose would also cover SEP revalidation (cross credit)?
The answer is Yes however in accordance with the latest ANO amendment
http://opsi.gov.uk/si/si2007/uksi_20073467_en_1 To convert a pilot to the SLMG he will need to pass a GSTwith an Examiner after you have finished the training, exactly as it used to be.
my CRI rating does not contain any clauses preventing me doing applied instrument training or aerobatics, as might appear on most freshly-minted FI(R) ratings.
No but as this is a JAA rating; you would also have to hold a IRI rating in order to teach applied IF. The aerobatics is quite legal but then anyone can legally teach aerobatics as it is not for the issue of a licence or rating!