Hi All,
got an answer from SAP Support and ICM restart isn't requrired anymore since >= NetWeaver 710.
Please see SAP Note 510007 - Setting up SSL on Web Application Server ABAP under:
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When, as of NetWeaver 710, you save or overwrite an SSL PSE, STRUST signals the PSE change to the icman, whereby the PSEs used for SSL are reloaded at runtime. Existing communication connections are not impaired as a result. However, all SSL session caches are emptied in icman so that all new SSL connections go through a complete SSL Handshake. On servers with a very large number of simultaneous connections, this could lead to an increase in the CPU load and increased response times.
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You are able to see respective information's as well at ICM trace.
Regards,
Jochen