data.table assigning output to a variable column

So I have a loop that I want to implement which assigns the original value (in row a and col b) + 1 if the value (at row a and col b) is equal to a certain number, however, when i try to assign the number using with = FALSE, I am unable to do so, and removing it yields me an output where the whole col is = to original value (in row a and col b) + 1.

Test Case:

a <- rep(0,6)
b <- 1:6
c <- -3:2
d <- runif(6)
e <-runif(6)
dt1 <- data.table("ID" = b,"code_a" = a,"code_c" = c, "code_d" = d, "code_e" = e)
dt1
   ID code_a code_c    code_d      code_e
1:  1      0     -3 0.5369538 0.269854945
2:  2      0     -2 0.7186787 0.009384648
3:  3      0     -1 0.8053726 0.831286263
4:  4      0      0 0.2084106 0.171294349
5:  5      0      1 0.0130021 0.730679582
6:  6      0      2 0.2902858 0.062175009

So in the following I have assigned ctr <- 1 and tested the scenario that I wanted to replace col_2 and row_1 with the number 1, but unfortunately, neither scenario is my desired output.

My Attempt number 1:

dt1[,eval(ctr+1), with = FALSE][ctr] <- 1

Error in `[<-.data.table`(`*tmp*`, , eval(ctr + 1), with = FALSE, value = list( : 
  unused argument (with = FALSE)

My Attempt number 2:

dt1[,eval(ctr+1)][ctr] <- 1
> dt1
   ID code_a code_c    code_d      code_e
1:  1      1     -3 0.5369538 0.269854945
2:  2      1     -2 0.7186787 0.009384648
3:  3      1     -1 0.8053726 0.831286263
4:  4      1      0 0.2084106 0.171294349
5:  5      1      1 0.0130021 0.730679582
6:  6      1      2 0.2902858 0.062175009

Desired Output:

   ID code_a code_c    code_d      code_e
1:  1      1     -3 0.5369538 0.269854945
2:  2      0     -2 0.7186787 0.009384648
3:  3      0     -1 0.8053726 0.831286263
4:  4      0      0 0.2084106 0.171294349
5:  5      0      1 0.0130021 0.730679582
6:  6      0      2 0.2902858 0.062175009

This is probably asked before, but I am unable to find the correct way to find the thread that asked this question. I also tried using ..ctr but to no success. If anyone can help me understand whats going on, it would be greatly appreciated.