Every agency has prerequisites for training courses. In many cases, an explanation of equivalent acceptable certifications is given.
For Tec45, the requirement is:
1. Certified as a Tec 40 diver or provide a qualifying certification from
another training organization. For the purposes of this level, a qualifying
technical certification is one that qualifies the student to make limited
decompression dives to 40 metres/130 feet using air and EANx using open
circuit scuba equipment.
I can't recall seeing a prerequisite specified for completing TecRec 40/45/50 training in sidemount. The sidemount course itself states that,once completed, all further PADI and TecRec courses can be completed in sidemount, where the instructor is also qualified in sidemount.
However, in general, PADI don't accept 'self-taught' in lieu of required prerequisite certifications...not at any level. Few agencies do...
I think it's quite reasonable that an instructor should seek proof of training in a given configuration before accepting a student onto a technical level course. If you're self taught, how can you
prove that you effectively learned all the necessary skills and drills to an appropriate standard?
There's no scuba police for fun diving... but on a training course you're under the supervision of that instructor. He takes liability for you... and also takes some personal risk accompanying you on decompression dives. In that respect, he has a duty of care to both you and himself. He also has legal liability should something go wrong.
The best option is to ask the instructor about your option to integrate Tec Sidemount training
into the Tec40/45/50 courses. PADI allow Tec Sidemount and Tec40/45/50 to be integrated, as the equipment aspect of the syllabus is near identical in both courses. This cuts down the unnecessary stuff... and expense...and also gives you some skills that don't feature on recreational level sidemount training.
For details on integrating sidemount and tec courses, read
HERE.
I've run many integrated courses and they're very successful. The courses compliment each-other well and integrating them simply cuts out replication of the same skills (i.e. air-sharing, shut-downs etc). The Tec Sidemount syllabus adds a few extra skills like feather breathing and reg swapping. Nice stuff to know. If you didn't have basic sidemount qualification, you'd do 2x two cylinder dives... then progress to 3 (the Tec40/45 dives). Then you'd do a 4 cylinder dive (beyond Tec40 scope). Most of my students take this option
even if they hold basic sidemount certification.
In a nutshell, the integrated course adds a second confined session and two further dives. It runs as:
Confined #1 - Tec45 confined plus Tec Sidemount confined pt1
Dive #1 Tec45 #1 plus Tec Sidemount #1
Dive #2 Tec45 #2 plus Tec Sidemount #2
Dive #3 Tec45 #3 plus Tec Sidemount #3
Dive #4 Tec 45 (deco dive)
Confined #2 - Tec Sidemount Confined pt2 (
can be done at the start...)
Dive #5 Tec Sidemount Dive #4 (3 tank sim deco)
Dive #6 Tec Sidemount Dive #5 (4 tank sim deco)