The Shia view is the following:
The dhikr being recited after every salat - 34x Allahu Akbar, 33x Alhamdulillah, 33x Subhanallah and 1x La illaha illallah- was taught by the Prophet to his daughter Fatimah and is known as Tasbeeh of Fatimah.
As everything the Prophet said and taught to people was inspired by Allah swt, it can be concluded that this tasbeeh is a divine recommendation to benefit its reciter.
It has immense significance in the eyes of the infallible Imams (a.s.) and the Shiite jurists. It is a simple ,short yet very powerful act of worship from the aspect of performance; its effect, reward and merit are abundant.
To gain the described rewards and merits, we must not alter the tasbeeh but stick to its exact form. For this reason, we do not add Mashallah to it.