A footballer selling hair ties sounds like a novelty. It is a textbook brand extension, and the legal work behind it decides whether it makes money or merely attracts copies.
What is being sold
Not an accessory. An association. The product works because a recognizable person uses it visibly, and consumers buy the connection. That connection is built from a personal name, an image, and often a distinctive product appearance.
The three rights involved
Trademark over the product name and the athlete name, filed in class 26 for hair accessories and any adjacent class. Image rights, licensed in writing from the individual to the company selling the product. Industrial design where the product itself has a distinctive appearance worth protecting.
Where these ventures go wrong
The product launches on the strength of attention, sells out, and within weeks marketplaces are full of copies. Without a registration there is no takedown mechanism, because platforms act on registration numbers rather than on explanations.
If you are planning a brand extension
File in the new class before you launch, not after. Your existing registration for one category does not cover a different one, and the window between announcement and copy is now measured in days.
Extending a brand into a new class
Protection reaches the goods and services you registered, so moving into a new product line means a new application, not a note on the existing file. Each class is a separate application with its own fee.
Before filing, the question is whether the new class is clear: the search has to cover the class you are entering, not the one you already hold, and the grounds in article 173 of the Mexican Industrial Property Law are assessed there.
Resist the temptation to register everything at once. Each registration you obtain carries its own declaration of real and effective use at the third anniversary, and protection continues only for the goods or services actually declared (article 233). A defensive class you never trade in is a class you will lose, having paid for it twice.