Extended IO registers handling in AVR using Assembly language

IN/OUT/SBI/CBI are just shortcuts for ST/LD family instructions (plus additional operations in the case of the latter), for addresses within the IO range. The IO range is very limited; registers outside that range, must use regular SRAM access. This is a common oversight, so this seems relevant here.

But you're already using LDS and STS to access registers outside that range; it seems you do know this. So I'm not sure precisely what you're asking. Then, you know how to read-modify-write, right?:

For example, avr-gcc 13 compiles

 ADCSRA |= 1 << ADIF; 

into

 ldi r30,lo8(122) ldi r31,0 ld r24,Z ori r24,lo8(16) st Z,r24 

Of course if you're already using Z, you can use LDS/STS directly; same code size (and, cycle count I think?).

Finally, as mentioned in the other answer, a read-modify-write is not actually required for this register; the bit is already set and you can simply read then write. Convenient!

Indeed, if you already know the value of the other bits of ADCSRA, you don't need to read it at all (and, generally settings aren't changing, so this can indeed be used in practice).

Or if the values are changing (say, stopping ADC after a series of acquisitions, to save power), I suppose you can write them back at the same time; unless there's errata that says not to.

(Semantics: note the above instructions are not a direct substitute for SBI/CBI, as they are not atomic; a truer emulation would wrap the passage in CLI...SEI (depending on initial I flag state), but this only accounts for software atomicity. Nothing can be done to account for register atomicity -- but AVR peripherals are at least reasonably well behaved, and we're generally fine with this.)