add_overall.tbl_custom_summary.md
In gtsummary: Presentation-Ready Data Summary and Analytic Result Tables

add_overall.tbl_custom_summary() works

Code
  as.data.frame(add_overall(tbl_custom_summary(trial, include = c("stage", "grade"), by = "trt", stat_fns = everything() ~
    my_stats, type = everything() ~ "continuous2", statistic = everything() ~ "S: {marker_sum}")))
Output
    **Characteristic** **Overall**  \nN = 200 **Drug A**  \nN = 98 **Drug B**  \nN = 102
  1            T Stage                   <NA>                 <NA>                  <NA>
  2      S: marker_sum                 S: 174                S: 94                 S: 80
  3              Grade                   <NA>                 <NA>                  <NA>
  4      S: marker_sum                 S: 174                S: 94                 S: 80