Split values from one category into two others by proportion, round down, remainder to one

General
1

I have this table, and I want to reassign the case counts when the cause is C55. I want to redistribute it mathematically according to the proportion between C53 and C54 (that is, if both have 1, assign 50% of C55 to each). Always round down, and if there is any remaining whole number, assign it to C53. This should all be done separately for each age group.

# A tibble: 26 × 4
    GENRE CAUSA GRUPEDAD CUENTA
   <dbl> <chr> <chr>     <dbl>
 1     2 C55   55 a 59       1
 2     2 C54   70 a 74       1
 3     2 C54   80 y mas      1
 4     2 C53   45 a 49       5
 5     2 C54   60 a 64       1
 6     2 C53   50 a 54       1
 7     2 C53   80 y mas      2
 8     2 C54   55 a 59       1
 9     2 C53   65 a 69       3
10     2 C55   75 a 79       3
# ℹ 16 more rows
2

Please post the entire data set in an easily copied format since it only has 26 rows. If your data frame is named DF, run

dput(DF)

and post the output.