I'm looking for a way to encode an epoch date / time into an existing string.

Let's say I have a string abcdefghijklmnopqrstuvwxyz and a datetime 1463134905, I need to be able to convert the string into something so that I can retrieve the date from it again and the original datetime.

Using XOR is not an option since I need to know the datetime in order to get the datetime out of it again.

abcdefghijklmnopqrstuvwxyz XOR 1463134905 => result
result XOR 1463134905 => abcdefghijklmnopqrstuvwxyz

So

abcdefghijklmnopqrstuvwxyz (someoperation) 1463134905 => someoutput

Now I want to be able to do

someoutput (someotheroperation1) => 1463134905
someoutput (someotheroperation2) => abcdefghijklmnopqrstuvwxyz

I know I'm adding extra data to the string, so if someoutput needs to become slightly longer, that's also fine, but max 1 or 2 characters, not by the length of the datetime epoch string.

So does a transformation exists that allows me to compact a datetime inside a string and somehow retrieve both the original string and the datetime without increasing the string size by much.

I know Burrows and Wheeler managed to mostly sort a string and unsort it again only storing 1 bit. I'm looking for an algorithm that, just like BWT, can completely change a string and return the original strings.