Hi Dave,
This amount of rework, particularly at LF-temperatures, is not a good idea as 
you surmised. That can consume upwards of 30% of the fatigue life of the 
vias, provided they survive the procedure.
If you indeed to 'cold' solder joints—this would mean SJs near the BGA 
centers, you need to 'up' the soldering profile. Reworking these is quite hard to 
do, bnecause it is difficult to get sufficient heat under the BGAs—that is the 
reason why vapor phase soldering is making a come-back.

Werner



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