Define categories for aspirated and unaspirated voiced stops, voiceless stops, and fricatives:
(I’m forced to use strange characters for each of these phones due to the one-character-per-phone restriction of SCA².)
Then Grimm’s law can be reversed as follows:
(As far as I can tell, PIE had none of /ɸ θ x xʷ/. ...
It depends on the word in question. Not that many English speakers would recognise laser as an acronym, so it has effectively become a 'normal' word. And it can be inflected, as in She was lasering away that old tattoo.
It is different for acronyms that are spelled all in upper case, I think; NATO is kind of 'frozen' in that respect, and I doubt it will ever ...
If you want to be strict, coerce them into your phonological rules.
Macy's: that would fit as macys; if /y/ is not a vowel, then macis
Outback: start with a consonant, so use one that is not too pronounced, such as /h/: hotback [*]. Also drop the /u/ from the diphthong. Or use hatback if your /a/ is pronounced more open (in that case hatbeck might work ...