I have SOLVED your problem, in which you can verify with https://www.epochconverter.com/, and I also have you to thank for that because it was this example, "30 + (23 x 60) + (11 x 3600) + (360 x 86400) + ((2022 - 1900) - 70) x 31536000 + ... etc", provided by you, was what made it successful, given that I had been searching the net for info. I wasn't aware that %my_year% (aka %tm_year%), excluding when you have to acquire total days of the year (i.e. tm_yday), had to be subtracted by 1900. Moreover, I solved your "tm_yday" issue using your $add($if(x,y,z),%my_day%). Nonetheless, here is the FULL SINGLE-line string to calculate EPOCH time, as well as the legends below the script, and when you employ it, per the example that you provided, which was "2022-12-26 11:23:30", your ANSWER will definitely be "1672053810".
Using, $add(A,B,C,D,E,F,'-'G,H):
$add(%my_second%,$mul(%my_minute%,60),$mul(%my_hour%,3600),$mul($add($if($eql(365,$regexp($num(%my_year%,4),'^((?:(?<![\d])(?:(?:[1-9][0-9]{2,}|[0-9]{2})(?:[13579][0-13-57-9]|[02468][1-35-79])|(?:[13579][0-13-57-9]|[02468][1-35-79]|[1-9](?:[0-9]{1,})?(?:[13579][0-13-57-9]|[02468][1-35-79])){1}00){1}(?![\d])){1})$',365)),$sub($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp(%my_month%,'^0*[01]$',0),'^0*2$',31),'^0*3$',59),'^0*4$',90),'^0*5$',120),'^0*6$',151),'^0*7$',181),'^0*8$',212),'^0*9$',243),'^0*10$',273),'^0*11$',304),'^0*12$',334),1),$sub($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp(%my_month%,'^0*[01]$',0),'^0*2$',31),'^0*3$',60),'^0*4$',91),'^0*5$',121),'^0*6$',152),'^0*7$',182),'^0*8$',213),'^0*9$',244),'^0*10$',274),'^0*11$',305),'^0*12$',335),1)),%my_day%),86400),$mul($sub($sub(%my_year%,1900),70),31536000),$mul($div($sub($sub(%my_year%,1900),69),4),86400),'-'$mul($div($sub($sub(%my_year%,1900),1),100),86400),$mul($div($add($sub(%my_year%,1900),299),400),86400))
YYYY-MM-DD HH:MM:SS (I am assuming that "YYYY-MM-DD HH:MM:SS" is UTC), where:
⯄ "YYYY" = "%my_year%" or "%tm_year%"
⯄ "MM" = "%my_month%" (aka FIRST half to solve for tm_yday)
⯄ "DD" = "%my_day%" (aka SECOND half to solve for tm_yday)
⯄ "HH" = "%my_hour%" or "%tm_hour%"
⯄ "MM" = "%my_minute%" or "%tm_min%"
⯄ "SS" = "%my_second%" or "%tm_sec%"
⯄ "tm_yday" ⟷ $add($if(x,$regexp($regexp(%my_month%,'^0*[01]$',0),'^0*2$',31)....,z),%my_day%) = "$add($if($eql(365,$regexp($num(%my_year%,4),'^((?:(?<![\d])(?:(?:[1-9][0-9]{2,}|[0-9]{2})(?:[13579][0-13-57-9]|[02468][1-35-79])|(?:[13579][0-13-57-9]|[02468][1-35-79]|[1-9](?:[0-9]{1,})?(?:[13579][0-13-57-9]|[02468][1-35-79])){1}00){1}(?![\d])){1})$',365)),$sub($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp(%my_month%,'^0*[01]$',0),'^0*2$',31),'^0*3$',59),'^0*4$',90),'^0*5$',120),'^0*6$',151),'^0*7$',181),'^0*8$',212),'^0*9$',243),'^0*10$',273),'^0*11$',304),'^0*12$',334),1),$sub($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp($regexp(%my_month%,'^0*[01]$',0),'^0*2$',31),'^0*3$',60),'^0*4$',91),'^0*5$',121),'^0*6$',152),'^0*7$',182),'^0*8$',213),'^0*9$',244),'^0*10$',274),'^0*11$',305),'^0*12$',335),1)),%my_day%)"
In hindsight, I have created multiple strings such as strings that can read time formats like "YYYY-MM-DD HH:MM:SS[-+]HH:MM", as well as strings allowing, for example, 2022-13-25 09:43:20, where the month, "13" (or time is 3 digits or higher), and the year, "2022", will be AUTOMATICALLY be adjusted to "2023" and "January" (aka "01"), accordingly, and since you didn't specify, I am only including the simple string. Moreover, I use this string for column sorting via regular expression: "tm_sec" (aka "%my_second%") ＝ "$regexp(%creation_time%,'^(?<![\d])(\d{4,})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2})[Z](?=$)',$6,1)". The "$if($eql(365,$regexp($num(%my_year%,4)....", which is the "x" of the "$add($if(x,y,z),%my_day%)", is the EXCLUSIVE to NORMAL years (aka 365 days), while the "z" is for the LEAP year (basically, anything that is not "365 days").
Now, I need help you. Do you know the formula to change/convert EPOCH time BACK into "YYYY-MM-DD HH:MM:SS", or just the Month, Day, and Year, given that hours, minutes, and seconds are easy to manipulate? I would really APPRECIATE that piece of information to accomplish an action file, making it whole. If you can find that information, just like the script above, I think that I can make it Mp3Tag compatible.