No, Thank You!

At the conclave, "The cardinal dean, or the cardinal who is 1st in order and seniority, in the name of the whole college of electors, then asks the consent   of the one elected in the following words :Do you accept your canonical election as Supreme Pontiff?"

Can he say, "No, thanks, I appreciate it but not at this time."? Yes, he can. But more likely, if a cardinal did not want to be Pope he would let it be known in advance of the vote.

Which brings us to Cardinal Giovanni Colombo. Archbishop of Milan. In the conclave of October 1978, Cardinal Colombo had garnered a number of votes as a compromise candidate (instead of  Cardinal Guiseppi Siri of Genoa and Cardinal Giovanni Benelli, Archbishop of Florence). Cardinal Colombo made it clear he would NOT accept the Papacy, paving the way for the election of Cardinal Karol Wojtyla.