no further changes on the proposed schedule are not acceptable

No, your sentence is not correct. 

All sentences begin with a capital letter.
All sentences end with punctuation.  Your choices are a period, a question mark, or an exclamation point.

What you also have here is a double negative. 
No further changes are not acceptable = all further changes are acceptable

While a double negative can be appropriately used to make a point, it does not work for your sentence.  You need to delete one of the negatives.

Further changes on the proposed schedule are not acceptable. 
No further changes on the proposed schedule are acceptable. 
 

I do want to add that if changes are no longer acceptable, the schedule isn't really proposed anymore, is it? 

The schedule is now set.  No further changes are acceptable.