Upvote:0
The UK is not part of the Schengen area; you'll need to obtain a separate visa for the UK if you plan to attend a conference there.
Therefore, changing your itinerary has no impact on your Schengen visa as it is not valid for the UK.
Note that you should apply for the UK visa from Malaysia and not plan on applying for it from the UK Embassy in France.
Upvote:2
It means another exit/entry so it could be an issue if you had a single-entry visa. But with a multiple-entry visa, it should be fine.
For more on changing your plans after you received a Schengen visa, you can have a look at Change of plans in Schengen visa and the links therein.
Regarding the UK visa you will also have to obtain, see Where can a tourist apply for a UK Visitor (standard) Visa? and UK Tourist Visa for Indian Citizens from Paris