On most arduinos, just do upload using programmer, with an ISP programmer of your choice connected.
However some Trinket-like (ie, ATtiny85 with VUSB bootloader) boards blow RSTDISBL making it impossible to program them via ISP without resetting that with an HV programmer, which most of us don't have. The official board doesn't do this - but make sure the ones you're buying don't.