Peace be upon you. Regarding the question of whether it is permissible to express political slogans during mourning rituals, both Grand Ayatollah Sayyid Sistani and Grand Ayatollah Sayyid Khamenei have stated that it is allowed. For further details, you can refer to the sources: Ayatollah Sistani's commentary on 'Al-Urwah Al-Wuthqa' and a specific inquiry addressed to Ayatollah Khamenei. May you be successful in all good.