that's quite the opposite, no ? The push operator is 04 and the pushed data is 2e786563 (pushop is also more explicit than push imo)

if (firstByte === opReturn.OP_PUSHDATA1) {
        // Save OP code
        pushdataOp = opReturn.OP_PUSHDATA1;

if (firstByte === opReturn.OP_PUSHDATA2) {
        // The next two bytes contain the number of bytes to be pushed onto the stack in little endian order.

        // Save OP code
        pushdataOp = opReturn.OP_PUSHDATA2;

if (firstByte === opReturn.OP_PUSHDATA4) {
        // The next four bytes contain the number of bytes to be pushed onto the stack in little endian order.

        // Save OP code
        pushdataOp = opReturn.OP_PUSHDATA4;

Please read your code. This kind of absurd pattern should not show up during diff review. Just looking at your code should make it obvious that this needs to be refactored.

This is backwards push is the actual data

as per the following code, pushOpCode would be a better name than firstByte

imo you should return the opcode in pushedWith. The value didn't appear on stack on its own

you already have pushedBytecountHex, you don't need pushedBytecountDecimal. Just set it once before use with no intermediate variable. If you think about it, the endianness is not an issue.

Why is that a special case and not the standard workflow ?

Wow, look at how much cleaner this code is now!

Nit: technically you have a push opcode but no pushed byte count, so it should be the opposite:

pushedWith: `${pushOpCode}${pushOpCode !== pushBytecountHex ? pushBytecountHex : ''}`

In any case please add a comment to explain why this is needed, as it may trigger you in the distant future.