In fact I got motivated enough to replace the resonator on my Uno board, partly to see how tricky it was to do.
Here's the board before modding it:
Then I desoldered the resonator and the unnecesary resistor:
Had some 22pF SM caps (0805 size, about the smallest I like to solder 
And the crystal - there seemed to be insufficient clearance for the standard 49U package from the caps (they weren't tiny enough!) but I wanted it clear of the bare resonator pads anyway to avoid shorts so its sticking up a little from the board:
Finally at some point I will add a blob of glue from a hot-glue gun to support it better mechanically. Overall not too fiddly if you have tackled SM components before. A solder sucker is required to clear the thru-holes for the crystal leads, the tiny resonator and resistor can be heated on alternate sides till it moves and can be pushed off the pads. Only attempt at your own risk of course 