is it possible to just update the baseline on specific task instead of changing whole baseline?
Baseline is a snapshot of the whole project state. I don’t understand what do you mean as “update baseline”. Baselines are not updatable by definition.
You are right the baseline should be a snapshot as this is used to compare with the actual execution. but in some of case, a new task may be created or exist task may be adjusted(e.g. original plan is not realistic, so this update just reflect to the plan which was not made correctly and it’s not a responsibility of task owner). This is similar feature that MSProject offers that it can save selected task to baseline rather than save all the tasks.