ArduinoISP, bootloading and clock source/frequency, fuses

If I use ArduinoISP to bootload a chip with the Uno bootloader (16 MHz xtal), to have one as a spare, is it possible to use the ArduinoISP to bootload it with the standalone 8 MHz internal clock bootloader later on?
Or will the chip still be dependent on external clock during bootloading?

This should work for you no problem. Reflashing without a clock source connected should make it all hunky-dory.

But if it is configured to use external 16 MHz clock like on Uno, can I still burn a bootloader for 8 MHz internal clock without a crystal, like explained here: http://arduino.cc/en/Tutorial/ArduinoToBreadboard ?

JanErik:
But if it is configured to use external 16 MHz clock like on Uno, can I still burn a bootloader for 8 MHz internal clock without a crystal, like explained here: http://arduino.cc/en/Tutorial/ArduinoToBreadboard ?

I believe the IDE bootloading procedure will first burn the proper fuse bytes for the board type you selected before trying to burn the bootloader code. So as long as you select a proper board type which will specify the clock source and speed (in your case one that specifies internal clock @ 8Mhz)the process should work fine no matter what prior bootloader had been installed in the target chip.