Conditional execution inside process chains

Has anybody a solution for implementing an "if ... else" inside a process chain?

Explanation:

we have about 50 process chains with very complex interdependencies which are triggered by an external job control system; we use therefore chains which contain local chains ("meta-chains");

we need the possibility to execute inside one chain some processes depending on the calendar (end of period processing), i.e. we need the possibility of a branch inside a chain, something like "if file 'flag_end_of_month' exist, execute this step else skip to next process"

We have investigated following possibilities:

- maintain start process with start by calendar (but this is not possible inside a meta-chain, you have to start the local chain with "Start Usind Meta Chain or API" which doesn't offer calendar conditions)

- use an abap which contains calendar processing (but the process type "abap" ends always unconditionally)

- use an external command (quirks!) (this offers a branch, but in the failure case the return code propagates to the rc of the hole chain, which is not good for our job scheduling system.

- create an own process type (has anybody already done something like this 😊