Tribunals usually frown upon Committees splitting bills merely to fit them within the Committee spending limits. This could be seen as being a ‘cheeky’ move by your Committee to avoid proper oversight by the OC.
The OC by-law needs to be correctly registered with the LPI and be entered on the Certificate of Title for the Common Property before it will become effective. It also needs to be passed by Special Resolution at the EGM.
In my opinion you would be bound by the old by-laws rather than the new if your renovations are passed at the upcoming General Meeting. There is, after all, no guarantee that the new Committee by-law will be approved by a special Resolution.
https://www.lpi.nsw.gov.au/about_lpi/strata_scheme_questions/new_bylaw_strata_scheme
I wouldn’t use the OC lawyer. You may need to go through the Tribunal to sort any difficulties out so, if I was you, I would seek independent advice. I would probably be seeking legal advice on this issue ASAP. Your renovations are extensive and expensive so to enable them to be achieved successfully in this environment of animosity it would probably be wise to seek legal advice sooner rather than later.