Looks like the sandbox-simplify command is removed in OS X sierra,
I can't find it in system path, only sandbox-exec command is available now.
So, is there any replacements?
It seems Apple is suggesting app developpers use this for their app, see man:
DESCRIPTION The sandbox-exec command is DEPRECATED. Developers who wish to sandbox an app should instead adopt the App Sandbox feature described in the App Sandbox Design Guide. It's in my opinion a misinformed and not showing security maturity on the part of Apple to remove security option from users and advise it to be dealt only by developpers.
What we've seen in the past is that a rare minority is usually pushing toward security improvement while the average developer see security as a roadblock rather than a value add.
Apple should revise their position and re-enable user-driven app policies. Especially they didn't disable it, they just made it much harder with removal of sandbox-simplify.
sad sad Apple, get a grip