Tory leadership hopeful David Davis has warned against "nip-and-tuck" politics in a dig against rival David Cameron.
The rivals are continuing their nationwide hustings
In the latest hustings between the pair, in London, Mr Davis said the choice was between "image-led politics" or "battle hardened experience".
Mr Cameron said he did not want to ditch key Tory principles but the party had to represent the country.
And he warned: "We cannot just play the same song, sing the same tune because we'll only lose again."
With the leadership race in its final fortnight, about 2,000 Conservative members attended the hustings event at Westminster Central Hall on Wednesday evening.
Party officials say about 60% of the members have now voted.
They say voting has been slower than in the 2001 leadership contest, perhaps because members are taking more time to listen to debates before making their choice.
Meanwhile, David Cameron received a boost from a YouGov poll on Wednesday night which suggested he was a more popular choice for prime minister than Tony Blair.
Some 41% of the 1,705 adults surveyed on Tuesday and Wednesdfay this week for Sky News wanted Mr Cameron in power, while 38% wanted to keep Mr Blair as leader.
Asked to pick between the two Conservative rivals, 37% opted for Mr Cameron and 20% for Mr Davis.
'No more tricks'
At the hustings event - in what will be seen as another attack on Mr Cameron's style - Mr Davis said his party had to change but in the right way.
"First, I do not believe that it is time to ditch our values or our principles," he said.
"Second, I do not believe that some quick, superficial makeover of our image - a Conservative equivalent of a Peter Mandelson-style rebranding - will put us on the path to victory.
"The public have had enough of such trickery.
"Our changes must be more fundamental and lasting than those wrought by calling in the political equivalent of the cosmetic surgeon.
"Nip-and-tuck politics are not for us."
Mr Cameron denies he is copying Tony Blair - and says he will not make the mistake of making policies to grab headlines.
He told Tory members he could deliver a unified team as he cited the senior figures who were backing his bid - including former leader William Hague.
"Wouldn't it be great to have William back as part of the team," he said.
But campaign aides stressed he was not suggesting Mr Hague had agreed to return to frontline politics.
As he left the event, Mr Cameron said he believed there was real momentum behind his campaign.
But asked if thought he had won the contest already, he replied: "No, I think it's wide open until those votes are counted. That's the great thing about democracy, but I'm still campaigning hard."