That is kind of weird.

Are you sure that, if you processed the ticket, the price doesn't jump when it actually comes to take payment? Some of those routes are available on other, better routings. For instance, a random search for SIN-BOM shows SIN-CGK-BOM on GA for 20k+€103, SIN-CGK-BKK-BOM on GA for 30k+€127 as well as SIN-CDG-BOM on AF for 153k+€153 (Flex Award).

I would be afraid that, even if you do get your SIN-CDG-(wherever) for so cheap that you would later be moved to a "better" routing.

I would advise extreme caution here - be prepared to eat the €45 cancellation fee if, having changed you, you are unable to convince them to cancel for free. [I would not advise, if they did change your routing, ringing up and demanding the original routing, I would just try to cancel]

I would certainly also NOT put my FB number in the separate CDG-NCE booking as this advises them that you never had the intention of taking your out-of-the-way routing (or I would fly easyjet!)

The usual advice should apply here: doing it once should be OK...but if they see a pattern of such behaviour on your account, then you quite likely would end up having your account audited, and the miles adjusted to account for what you actually flew - or have heavier sanctions imposed.