The question asks for a general answer but gives only one special context. In general, only and but only are not substitutable. *they but only work that way occasionally.

This will only happen if you go with me. This will happen only if you go with me. I am from bangalore and people here tend use the word only to emphasise something in a sentence. We are getting that only printed. What is the proper way to put it? Which is grammatically correct? I can only do so much in this time.

What is the proper way to put it? Which is grammatically correct? I can only do so much in this time. Or i can do only so much in this time. The oxford english dictionary defines but only (which can also occur as only but) as meaning ‘ (a) only, merely; (b) except only’, and comments that its use is now poetical.

(b) except only’, and comments that its use is now poetical.