Normally reading all cells as strings should do the trick

For sure the closed bracket ) behind sheet_name=None is wrong in you code

df_25_dict = pd.read_excel(2025_data, sheet_name=None),
    dtype={
        'bg_code': str,
        'tranx_date_year': str,
        'journal_number': str,
        'journal_line_number': str,
        'prj_code': str
    },
    parse_dates=['tranx_date', 'entry_date'])

Alternatively there is also the converters argument in Pandas read_excel() to control data type conversion better

https://pandas.pydata.org/docs/reference/api/pandas.read_excel.html

Python pandas: how to specify data types when reading an Excel file?