That is absolutely true.
And editing critical system files may bail out a few noob's N900

I do use a different approach:
put a script in event.d,
that checks for existence of my swap file (yes, I do use a swap file on standard vFAT SD partition (too lazy for repartitioning)), could also check for existence of partition.
then enable the swap as loopback device with higher priority (using bb power's swapon or also possible debians swapon). This way at startup eMMC swap is used, around 4-5MB, and then swap only on SD.
If you want to cleanup swap, just 'swapoff mmc' and it uses eMMC swap. If I want to use again swap on SD, just enable it with higher priority 'swapon mmc -p 0'. This assures also that swap is available even no or another SD is available.

As my script is highly customized to my needs ( starting python maps server, mounting maps in a loopback file, checking for other stuff) I am not going to post it here (in its current state) ...

I am not sure that using loopback as swap is faster (better) than using eMMC swap, but as there are no tools yet to confirm, it is just subjective opinion.