No. It was never implemented. The best you can do is to save as 7 which can of course be read by 7.5.
From:[hidden email] [mailto:[hidden email]] On Behalf Of Simon Nathan Sent: Tuesday, December 20, 2016 1:48 AM To: A mailing list for Sibelius plug-in developers <[hidden email]> Subject: [Plugin-dev] Save as 7.5
Quick question - is there a way to save a score as 7.5? The reference only goes as high as 7!