Is it permissible to adopt the view of another madhhab, previously unknown, in order to validate a prayer after an action that would have invalidated it according to the madhhab one adheres to?

If the intention is that you performed an act that invalidates prayer according to your madhhab, and then you became aware of its validity according to another recognized madhhab, then the issue relates to switching between madhhabs and following an opinion (taqleed) after the act has been performed. Some scholars permitted this, as long as the intention was not to merely seek out the dispensations (rukhs) of the madhhabs. Accordingly, there is no objection to following the opinion that affirms the validity of the prayer in this situation, provided there is no intent to indulge desires or pursue dispensations. Statements regarding this matter have been cited in books of fiqh, including what Ibn Abidin mentioned in "Radd al-Muhtar," and "Al-Insaf" by Shah Waliullah Dehlawi, and "Hawashi al-Shirwani."