What solder for low temp removal and resoldering to pcb
For chips that are hard to get off, I use low temp solder, then use a wick to clean up the remaining solder. It cleans off just like regular solder, if you clean it off good and put new solder on it.

The alloy contents of low temperature solders such as chip quick low temp solder (which is what I use) have a high bismuth content in them (specifically for one solder Sn42/Bi57.6/Ag0.4) this lowers the melting point, however it does make it more brittle.


  "All combinations involving bismuth were brittle, caused by the
  stiffening effect of solder due to the homogenized presence of bismuth
  in the joint, thus the brittle IMC interface became the weakest link
  upon shearing," said Ning-Cheng Lee, vice president of technology at
  Indium.  


Source: http://www.ipc.org/feature-article.aspx?aid=Improving-Reliability-with-Low-Temperature-Solders

Use the low temp solder and clean it off, then put better solder on. If regular solder cannot be applied after cleaning off then a different method of heating will need to be found or live with the risk of being brittle and use a solder with a high bismuth content.