Is it possible to read, modify and write back the modified value during a single 'touch' of a Mifare Classic card? All the tutorials only read or write during a single 'touch', not both. If so, are there any caveats that attention must be paid to?
With devices I've worked with (android with nxp controllers, hid omnikey and 6055b reader), yes. Naturally, a read and write will take longer than just a read but can be done in a reasonable amount of time