One more again : https://bugs.limesurvey.org/view.php?id=11519

This is from survey part : then can be in global replacement.

See : https://github.com/LimeSurvey/LimeSurvey/pull/545 one more again

Again one : https://www.limesurvey.org/forum/design-issues/107171-editing-registration-variables#142501

See https://bugs.limesurvey.org/view.php?id=11783 for a reason why i don't like new {REPLACEMENT} system.

In X month : we don't know what is it, where it's uses, how it's used.
A plugin have own clear documentation

Another solution : i EM

I think it's great if we can extend 'replacement' part : replace or add new KEYWORD
(i attach related bug some minute after)

But we try to remove event , then it's seems the best way is just to add :

1. A public function setKnowVar($var as string, $value=null as string|null)
2. Add it in LimesurveyApi

This fix partially, but after : we can have

1. Add a var in EM
2. Another system for another purpose (or same)

Still the issue with existing knowVars
Easys
If $var didn't exist : create it in readWrite->N mode (https://github.com/LimeSurvey/LimeSurvey/blob/develop/application/helpers/expressions/em_manager_helper.php#L3642)
If $var exist and is a "fixed var" : update code

if $var exist and is a dynamic var ( answer in fact) allow updating the actual value ? In DB + in $_SESSION ?

https://github.com/LimeSurvey/LimeSurvey/tree/develop/plugins/expressionFixedDbVar