Hello Fannur, 

I don't see a way to prevent an end user from adjusting the row height of a task. Doing so will adjust the chart side. You can iterate over your tasks and readjust them to a default height by using the CalendarInfo. Ultimately this is considered to be a new product idea.

 this.ultraGanttView1.CalendarInfo.Tasks[0].RowHeight

You can suggest new product ideas for future versions (or vote for existing ones) at <https://es.infragistics.com/community/ideas>.
Submitting your idea will allow you to communicate directly with our product management team, track the progress of your idea at any time, see how many votes it got, read comments from other developers in the community, and see if someone from the product team has additional questions for you.
Remember when submitting your idea to explain the context in which a feature would be used and why it is needed as well as anything that would prevent you from accomplishing this today. You can even add screenshots to build a stronger case. Remember that for your suggestion to be successful, you need other members of the community to vote for it. You can also link back to this thread for additional details.

Let me know if you have any questions.