pandas overwrite values in multiple columns at once based on condition of values in one column

You need series.str.len() after splitting to determining the length of the list , then you can compare and using .loc[] , assign the the list wherever condition matches:

df.loc[df['col1'].str.split(":").str.len()>2,['col1','col2','col3']]=["", "", False]
print(df)

---

   col0 col1    col2   col3  col4
0    11               False   elo
1    22  a:a     foo  False   foo
2     1    a  foobar   True   bar
3     5               False  dupa

Use Series.str.count, add 1, compare by Series.gt and assign list to filtered columns in list:

df.loc[df['col1'].str.count(":").add(1).gt(2), ['col1','col2','col3']] = ["", "", False]
print (df)
   col0 col1    col2   col3  col4
0    11               False   elo
1    22  a:a     foo  False   foo
2     1    a  foobar   True   bar
3     5               False  dupa

Another approach is Series.str.split with expand = True and DataFrame.count with axis=1.

df.loc[df['col1'].str.split(":",expand = True).count(axis=1).gt(2),['col1','col2','col3']]=["", "", False]
print(df)
   col0 col1    col2   col3  col4
0    11               False   elo
1    22  a:a     foo  False   foo
2     1    a  foobar   True   bar
3     5               False  dupa