There is a risk that the border officer might decide to revoke the visa under article 34(2) of the Schengen Visa Code:
A visa shall be revoked where it becomes evident that the conditions for issuing it are no longer met. A visa shall in principle be revoked by the competent authorities of the Member State which issued it. A visa may be revoked by the competent authorities of another Member State, in which case the authorities of the Member State that issued the visa shall be informed of such revocation.
Now the fact that you've called the German authorities in India and explained to them why your plans have changed would work in your favor, especially if you could prove this with some documentary evidence if you are challenged at the border. But since it was a phone call, I suppose you don't likely have any documentary evidence.
Article 34(3) provides that you the visa holder may ask for the visa to be revoked. The most transparent way, therefore, to travel to the Schengen area for tourism during the validity of this visa would be to request its revocation and apply for a new visa. If the official consular reaction is to tell you to use your existing visa instead, then you will have it in writing and be able to show it at the border.
There is another wrinkle here. It is related to your question
If yes, should this be to Germany as the first port of entry?
The first port of entry is not relevant. The country that is supposed to issue your visa is the country that is your main destination. So if you're going to a conference in Germany, and you find a more affordable flight through a different Schengen country, for example France, you should get your visa from Germany even though you are going to enter the Schengen area through France (but don't do this if the flight is operated by Turkish airlines). If you have a Schengen visa issued by Germany and the airline asks you about your main destination, and you say that it's something other than Germany, you could be denied boarding regardless of whether you're flying to Frankfurt or anywhere else.
Unfortunately, it is not particularly clear where the threshold is for judging whether "the conditions for issuing [a visa] are no longer met." The change in the purpose of your trip from business to tourism might or might not be a problem. A change in your main destination is far more likely to be.
If you can afford to undertake a tourist visit to Europe then the savings you would realize by repurposing this existing visa -- which would probably be below INR 10,000 -- are probably relatively insignificant in the face of the chance of being turned back at your point of departure, at your point of transit en route to the Schengen area (if any), or at passport control at your point of arrival.
To be clear, I think that chance is fairly small. It's probably far more likely than not that you would be able to make this trip without trouble. The cost of the negative outcome is high, however: the lost airfare, lost time, inconvenience, and disappointment are probably enough, and that is without even considering the effect on future visa applications and future travel.
If you think of asking for a new visa in this case as insurance protecting you against these negative outcomes, it's probably justified even if their probability is low.
