The point of my posts have been: which rules have been changed and what values do those changes reflect?
An examination of which rules have been changed in most institutions of western countries will reveal the same pattern of derangement - i.e. disturbance of order and function - by the same cultural forces in the same direction. (An example of one of these can be summed up as "boys should be more like girls or feminine.")
But schools having the power to set standards on grooming and similar can actually be useful in terms of resisting these trends.
These are pictures from the webpage of the school in question.

Looking at them, what do we see. Well, I see a separate boys and girls uniform (similar, but different - boys are wearing collar and tie, girls are wearing blouses). We see boys with short hair, 'typical' of boys, girls typically with longer hair. Separate PE uniforms too (and it looks like boys and girls are also different sports).
Having these rules, if they are used to do it, actually allows schools to ensure that the differences between the sexes are acknowledged and not blurred out of existence. Now, it isn't always done well - some schools deliberately go for unisex uniforms and unisex standards, for example. But it can be done well, and to me it looks like this school is one that does try to do it well.
Boys are expected to dress and look like boys. Girls are expected to dress and look like girls. At least to the extent that this can be achieved with clothing and grooming.
If this school wanted to eliminate the differences between boys and girls, it wouldn't have different uniforms for them, and different expectations about hair and similar.