My hands're dirty.

[ghoul]

Can I only use contractions for a set of preexisting contracted words or for any word actually?

The preexisting ones are of course known to me but I'm thinking about ones like my hands're dirty.
I could've sworn that I heard people use them similarly to how I've spelled it above, I may be wrong though. It certainly doesn't look like correct written english

 

[emsr2d2]

Can I only use contractions only for a set of pre-existing contracted words or for any words? actually?

The pre-existing ones are of course known to me but I'm thinking about ones like "My hands're dirty".

I could've sworn that I've heard people use them similarly to how I've spelled it above; I may be wrong though. It certainly doesn't look like correctly written English.

Note my corrections above. I would just about accept "hands're" if you were transcribing someone's speech. I certainly wouldn't use it in standard written English. Just remember that the person doesn't actually say "hands're". They say "hands are" but the "are" comes out like "uh".

 

[ghoul]

@emsr2d2 Thanks for your input and the corrections again.
Can we go over the underlying grammar rule for this example?

Can I only use contractions only for a set of pre-existing contracted words or for any words? actually?

I tried looking it up but didn't find a rule that supports your claim on the quick. I thought that in the above case the following rule would apply:
If the focus is on another part of the sentence, we usually put only in the normal mid position for adverbs (between the subject and the main verb, or after the modal verb or first auxiliary verb, or after be as a main verb), see https://dictionary.cambridge.org/us/grammar/british-grammar/only.

Regarding "pre-existing", a hyphen-less variant is possible according to this dictionary.

 

[5jj]

https://dictionary.cambridge.org/us/grammar/british-grammar/only.

I regard the examples below from the page you linked us to as less than perfect;

I only go home once a month.

She had only arrived at midnight the night before.

I would put the 'only' before the words it is restricting, 'once a month' in the first sentence, and 'the night before' in the second.