I strongly suggest calling reservation office and confirming your reservation status.

I have a terrible experience of last minutes flight change triggering no-show.

My original booking of DONEX is
------CDG-xLHR-DXB-LHR-JNB (CX issued ticket)

At CDG BA's checkin counter, I asked my CDG-LHR flight to an earlier one.
A checkin agent was happy to do so. However, He/She did make something wrong in my reservation.

I got CDG-LHR, and LHR-DXB boarding passes. At that point, no problem.
However a couple of days later, at DXB checking counter, an agent said I didn't have DXB-LHR reservation.
The record said a reservation of DXB-LHR-JNB was cancelled because of no-show.