I think all analyses are fine as long as you characterize them what they are (confirmatory, exploratory, fishing expedition). So, in the interest of conflict avoidance, I'd conduct and run the analyses and make sure that in the manuscript I qualify them as what they are (e.g., "On an exploratory note we deleted participants with high values from condition A. Eliminating five people yielded a significant effect. As this analysis was not pre-registered, however, we caution to base strong inferences on this exploratory finding."). If editors insist you should run these analyses and disguise them as if they were confirmatory, I would contact the editor in chief.