Yes.
He who BELIEVES presently has everlasting life, not the person who has stopped believing.
The security of salvation (Christ) is gained through your believing. Stop believing and you no longer have the security of Christ who is gained through believing/trusting in Him.
So the question really boils down to if you can stop believing or not. Well, if we couldn't Paul sure wasted a lot of time persuading the saved Galatians not to go back to the law in unbelief and become slaves to the law who don't inherit the kingdom, noting that only sons through faith in Christ are in line for the inheritance.
He who BELIEVES presently has everlasting life, not the person who has stopped believing.
The security of salvation (Christ) is gained through your believing. Stop believing and you no longer have the security of Christ who is gained through believing/trusting in Him.
So the question really boils down to if you can stop believing or not. Well, if we couldn't Paul sure wasted a lot of time persuading the saved Galatians not to go back to the law in unbelief and become slaves to the law who don't inherit the kingdom, noting that only sons through faith in Christ are in line for the inheritance.