ID <- c(1, 1, 2, 2, 3, 3, 4, 4, 5, 5)
    period<- c(1, 2, 1, 2, 1, 2, 1, 2, 1, 2)
    column1<- c(100, 400, 500, 300, 700, 800, 300, 100, 1100, 100)
    column2<- c(1500, 100,800,900,100,1100,1200,200,100,400)
    column3<- c(200, 1000, 200,NA,500,800,1100,300,100,2000)
    df<- data.frame(ID, period, column1, column2, column3)

ID period column1 column2 column3
1      1     100    1500     200
1      2     400     100    1000
2      1     500     800     200
2      2     300     900      NA
3      1     700     100     500
3      2     800    1100     800
4      1     300    1200    1100
4      2     100     200     300
5      1    1100     100     100
5      2     100     400    2000

agent_number<- c(100, 200, 300)
agent_name<- c("agent1", "agent2", "agent3")
lookup_table<- data.frame(agent_number, agent_name)

ID period column1 column2 column3 column4 column5 column6 column7
 1      1     100    1500     200       1  agent1  agent2    <NA>
 1      2     400     100    1000       1  agent1    <NA>    <NA>
 2      1     500     800     200       1  agent2    <NA>    <NA>
 2      2     300     900      NA       0  agent3    <NA>    <NA>
 3      1     700     100     500       1  agent1    <NA>    <NA>
 3      2     800    1100     800       0    <NA>    <NA>    <NA>
 4      1     300    1200    1100       1  agent3    <NA>    <NA>
 4      2     100     200     300       1  agent1  agent2  agent3
 5      1    1100     100     100       1  agent1  agent1    <NA>
 5      2     100     400    2000       1  agent1    <NA>    <NA>

agent_number<- c("100", "200", "300")
df %>% select(ID, column1:column3) %>%
mutate_at(vars(column1:column3),list(~ ifelse(. == agent_number, 1, 0)))

left_join(df, lookup_table, by=c("column1"="agent_number"), suffix = c("", ".1"), suffixes_mandatory = c(FALSE, TRUE))
left_join(df, lookup_table, by=c("column2"="agent_number"), suffix = c("", ".2"), suffixes_mandatory = c(FALSE, TRUE))
ID period column1 column2 column3 agent_name
 1      1     100    1500     200       <NA>
 1      2     400     100    1000       <NA>
 2      1     500     800     200       <NA>
 2      2     300     900      NA       <NA>
 3      1     700     100     500       <NA>
 3      2     800    1100     800       <NA>
 4      1     300    1200    1100       <NA>
 4      2     100     200     300       <NA>
 5      1    1100     100     100       <NA>
 5      2     100     400    2000       <NA>