Trial transcripts cannot be easily or ethically altered. Nonetheless if the court reporter has worked for the judge for many years, s/he may be in the habit of cleaning up his record a bit (grammar usually). If a judge asks a court reporter to change something of substance and s/he does then that would be a crime. But as the lawyer says it's difficult to prove.
One way that you might be able to prove it is to subpoena the original raw notes and/or audio tapes that the reporter used to produce the transcript. Some reporters use the stenographic machine, some repeat the testimony word-for-word into a recorder which is often backed up with a separate audio recorder.
By the way, it would be improper for there to be any deliberate modification of anything in the record, including cleaning up the judge's grammar. The reporter has a legal obligation to document the proceedings verbatim; she is not permitted to edit it in any manner or for any reason.