Not sure if it's just a Scottish thing (since i don't know many people who aren't Scottish), but why on earth wouldn't you just write the correct spelling when it has the same amount of letters as the wrong spelling?
I'm Scottish too, but i don't thing i've ever wrote in 'Scots' before. Lately, I've noticed a lot of my friends texting me in this way, or people's comments on FB.
Here's an excerpt of the latest convo on my newsfeed between my friend and someone he knows:
Yae doin anyhin tonight babez?
Naw, nuhin dawl. U uptae anyhin?
Naw kin a jist cum roon tae yours en?
Aye nae bother. Pm me.
WHY? I realise this is a very trivial thing, but i just don't get it. Surely it would be quicker to write 'No' than 'Naw'?