Learn Spanish (Latin America): Decidimos pintar la moto clásica a lo rebelde. - We decided to paint the classic motorcycle in a rebellious style.

The phrase a lo is used before an adjective or noun to mean "in the style of" or "like a". Here, a lo rebelde means "in a rebellious style". It acts as an adverbial phrase of manner, telling us exactly how they wanted the motorcycle to look.

Could I just say rebeldemente instead of a lo rebelde?

You could, but it changes the nuance. Rebeldemente implies the physical act of painting was done rebelliously (like defying your boss while holding the brush). A lo rebelde means the resulting style of the paint job itself is rebellious, emphasizing the aesthetic vibe.

Wait, why is it la moto clásica if moto ends in an -o?

Moto is short for motocicleta, which is feminine. Even when shortened, it keeps its feminine gender. That is why we use the feminine article la and the feminine adjective clásica. Other common examples you might remember are la foto (fotografía) and la radio (radiodifusión).

Decidimos translates to "we decided" here, but isn't that also the present tense for "we decide"?

Yes, it is! For regular -ir verbs like decidir, the first-person plural (nosotros) form is identical in both the present and the preterite (past) tense. Without other time markers in the sentence, you have to rely entirely on context to know if it means "we decide" or "we decided".