This O level hurdle is not a road block that you cannot cross. It is not a guillotine blade that severs all chances of you from ever being considered as a cadet.
If it is the only thing holding you back from being considered, then you must ask yourself, are you willing to fix it?
What will it cost you to retake the O's as a private candidate (in time and money terms)?
Will it cost more than doing a self-funded fATPL (especially with no promise of work at the end)?
How badly do you want to be considered?
These are the sort of questions you must ask yourself, for it is the same questions that the person screening your application will also ask.
Bascially - if you as a candidate can't f**king be bothered to do it, whether again or not, then why should SIA even consider you? The conditions are there, made known to you in advance, if you don't feel like complying but just want to make excuses, then do it on your own time.