This entire arc is about Akebi understanding what love is with it starting with her and Erika doing a confession scene
So far so good.
Erika wasn't wearing her hair in a ponytail when in chapter 56 Erika suggests she completely take on her role and Akebi responds that she will fall in love for real, nor is Erika wearing a ponytail in the next chapter when they act out a fairly romantic scene, nor is Erika wearing a ponytail in chapter 66 when Akebi asks Erika to watch her and tell her if she touched her heart.
It doesn't mean their "method acting" began the moment Erika put up the ponytail. Other than that, just look at chapter 71 page 7, when Erika says "
I wont be able to stay this close and touch you much longer". How would you imply it given the context of the play? Are these just dialogue they train? Or are these also Erika's true feelings? Erika knows that the play is a pretext, and a good chance, to get closer to Akebi. I do kind of think Erika is in love (ai, not koi) with Akebi and Erika has a firm understanding of her love to her.
On the other hand, we do not know 100% what shape Akebi's love takes for Erika. She can very well be serious in her love for Erika as a friend or in admiration (koi, not ai). This one-sided crush would otherwise warrant a yuri tag, would it not be for the actual chapters about girls having some kind of crush on another be so sparse. The girls' love tag here, in my opinion, has no meaning other than better searchability. After all, there is plenty of manga with Girls' love tags on here that are not yuri and i know many western readers have a problem wrapping their head around this matter.
Erika only puts her hair up in chapter 69, and that chapter isn't her changing her look in order to do method acting or whatever
I love how you disgregard the rest. Erika not only puts up a ponytail, she changes her clothing completely. Shirt, pants, ponytail. She looks boy-ish exactly why? Think about it. Who is the play about? This is not just her getting serious. This is a trope often seen in yuri.
For the ponytail symbolism to actually work as a means of "this is only acting, they do not feel this way for real", it would require both the play itself to be entirely different
If you followed until now you will understand why this does not check out. I see the points you are making, i just can not agree with them. Not because i want to be right ( i want
you to be right) but because i am just not convinced.
Lastly, if we look at official channels, Akebi-chan no sailor fuku is not tagged as yuri (yet). Do i wish it to be yuri (between Erika and Akebi)? YES. Do i know better than to pass judgement when the author left open a backdoor they can backtrack from yuri? "Oh, it was all just a play" as in "it was just a phase". No, i know indeed better. I hope you better understand why i am reluctant to call this yuri (yet).