Hierro was appointed in the wake of Lopetegui's dismissal on Wednesday for agreeing to take over Real Madrid following the World Cup without informing the Spanish football association, a drama that threw the team's preparations into disarray.
"We are not going to deviate one iota from our footballing concepts and what we've been doing for a long time now," the distinguished former Spain defender Hierro told a media conference in Sochi on Thursday.
"You're going to see the Spanish squad that you're used to, the Spanish squad that likes to be the protagonist in the match, that likes to play beautifully, and we have a very clear strategy in mind.
"We have a very clear goal in mind, we've worked for two solid weeks before the competition.
"We still have a lot of the coaching staff from before, we have our principles very clearly in mind, and we are not going to change that reality overnight."
Flanked by Spain captain Sergio Ramos, a relaxed Hierro, once the national team skipper himself, seemed to have put the turbulence of the previous 36 hours behind him as he stressed that little would change with him at the helm.
"We need to respect the work that has been carried out over the last two weeks in the run-up," the 50-year-old said.
"We respect the European champions (Portugal), we know that they have one of the best players in Ronaldo and a coach with experience, but we trust fully in our lads."
Describing their Group B games as "three finals", Hierro said that all 23 players would need to give their all if Spain were to succeed in Russia.
"To win this game we need to do our homework. We need to know that we are going in there fully fit and well-prepared. These last two weeks have been quite intense, but we have a clear idea of what we want to achieve tomorrow," he explained.
Even if he wanted to, Hierro is unlikely to have the time to change much about the Spanish style of play ahead of their first game.
"It's true we don't have much time to work with, so we're not going to change that much," Hierro said.
(Reporting by Philip O'Connor; Editing by Ian Chadband)
