Maybe, maybe not. First, although you are approved for $100,000, the lender will only lend up to the appraised value of the house minus your deposit. If the house appraises for $80,000, assuming an FHA with 3.5% down, you can borrow about $75,000. If the house were to appraise for $100,000 (highly unlikely, otherwise the seller would be asking for $100,000), then you could borrow about $95,000 and use the $15,000 extra for renovations.
If the house appraises for less than $80,000 and you can't get the seller to lower his price, then no matter how much you are approved for, you would have to come up with the difference - for example, if the house appraises for $75,000, not only do you need a down payment based in the $75,000 but you would also need the $5,000 in cash.
The house acts as collateral for the loan which is why you can only borrow up to the appraised price - which is the price the lender could expect to get for the house if you default and get foreclosed on.