void setTargetFileId(long fileId) throws IOException {
		if (versionFile == null) {
			throw new IOException("Version file is closed");
		}
		if (readOnly) {
			throw new IOException("Version file is read-only");	
		}
		targetFileId = fileId;
	}
Change the file ID associated with the buffer file to which this version 
file can be applied.
@param fileId file ID
Ghidra/Framework/DB/src/main/java/db/buffers/VersionFile.java