Are they vintage 25W Celestions? If they're in good shape, a 4x12 with greenbacks 'should' be able to handle (and I believe it's rated for 100w). FWIW, I gigged with a 50W Marshall for several years w/ a 1x12 cabinet and a 25W Celestion, and often times dimed it with no problems. I also profiled my 100W Marshall through my 4x12 with a mix of vintage and reissue Celestions...and again no issue (and the amp was on 10).
Your mileage may vary depending on how much your amp is putting out and the condition of your speakers....so proceed with caution and at your own risk!!
That being said, I've never personally had an issue cranking my 100 through a 4x12, and think it would be unlikely to cause any damage for the short time it takes to profile. You also get a different sound than you would with two 4x12 cabinets, because with a single cabinet, the speakers are driven harder and have more cone breakup, which is desirable to my ears.