No he didn't. He explicitly stated that there will no further changes permitted to the rubbish deal obtained by Cameron in February.
http://uk.reuters.com/article/uk-britain-eu-juncker-idUKKCN0Z81G4
EXACT words:
"British policymakers and British voters have to know that there will be no kind of renegotiation," Juncker said of the deal on Feb. 20 that gave Britain an explicit exemption from the founding goal of "ever closer union", offered concessions on the welfare rights of migrant workers and safeguards for the City of London financial centre.
"We have concluded a deal with the prime minister. He got the maximum he could receive and we gave the maximum we could give. So there will be no renegotiation, not on the agreement we found in February, nor as far as any kind of treaty negotiations are concerned," Juncker said.