I have applied for an Indian tourist visa not knowing I clicked travel by road via Haridashpur. Am I still able to travel by air?
Are there any conditions applied to your visa? Does it day you can enter only though particular cities or via a particular mode of transport? If not, you're good to go.
Some Indian visas are indeed restricted in those aspects but those restrictions are mentioned on the visa.
When you apply, they ask for your itinerary. Many countries do (Russia for example). However, it's more to get an idea of what you're planning, to see if it's feasible (eg have you thought it through) than a hard and fast "you must do this".
Once approved, you can change. We did while driving autorickshaws - they go slower than expected and people got sick. What if there's a traffic jam, or an accident and you can't make your planned itinerary. It's reasonable to change. Just make sure your insurance knows about it, and if you let your government know, as many do (eg SmartTraveller in Australia), make sure you update that.