The CONFIG word is read or programmed by your programmer (PIckit2 or 3, etc.) when you read the chip initially. The programmer can read the CONFIG word and you can save it. In coding, the default in Oshonsoft Basic compiler is to set "Highest Voltage", which is both BG bits set high. However, according to datasheet, those bits are set at the factory and should be preserved.
Same with OSCCAL, it will be wiped when programming or erasing. Read the value first, and save it. A Pickit2 or 3 programmer will have a calibration routine to reset that value, based on timing tests it loads into the PIC (erases your code to calibrate).
Sorry, I don't use the 12f629, I use the 12F675 just instead in case I need an analog input.