No problem. I've had several tickets reissued as electronic from paper and it is a flawless process. Seems to be better/smoother than freshly issued e-tickets. AA is doing this for all available routings (AA, BA, CX, QF can take etickets, IB, LA, AY and EI cannot as of last month). But keep a record of your ticket number as well as the PNR -- you will need the ticket number if something does go wrong, the PNR is not enough.