If playing an original, you should not have any issues, as they are correct.  It is flawed backups they detect, incorrect sector information, Wave1-4 failures, and so on.  Even then, if they ever decide to do more tests, that firmware adjusts for, they could tell it's modded, only by the responses given.  CFWs are designed to give readings they expect, but if the response is to fast, to slow, or shows no variation, they can tell.

IT was mentioned M$ started doing read tests, because people were limiting the drive speed with FCWs.  If they do a read test on a portion of the disc where read speed it optimal, they expect a 10x read, and they only get 4x because you used 4x firmware, it fails.  That would also read the originals at 4x, because the firmware is SET to only read at that speed. 

They are not doing everything they can to curtail modding, they gradually increase their security every year. 

Just keep in mind that you CAN be banned any time, for any reason, that way you're not surprised if it happens.

There are mod-chips, which is the way I plan to go eventually.  I pay for all my games, I end up with 100+ games at the end of the console's life cycle.  I make backups, and put the originals away, then eventually sell them all off, with the console. 

I think there is a Modchip that detects originals, and shuts off...