First I will ask do you really need such a long page name as 255 characters are quite a long string already, and it is very difficult to read in Workspace projects.
As your page name comes from URL, you can look at the URL structure to see if there is anything that can be omitted or shortened. Using the URL of this thread as an example: https://experienceleaguecommunities.adobe.com/t5/adobe-analytics-questions/clarification-on-classification-usage/td-p/577430. The whole "https://experienceleaguecommunities.adobe.com" can be turned into "ELC", "t5" is not required, "adobe-analytics-questions" can be "AAQ", the remaining are dynamic from the question title can be turned into the code "577430" only.
As you can pass in custom page names, the above conversion can help to shorten the page name dramatically.
As mentioned by @mandygeorge that there are still character limits on classification so it cannot help you and you also need to regularly and manually upload the classification text which is problematic. There is API to upload but which is AA API 1.4 and no corresponding API in the AA API 2.0, so not a reliable approach.
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So if such a long page name is absolutely required, I will use 2 eVar to store them. The first eVar store up to a certain level of structure, like "hostname:top_level:2nd_level", then a second eVar stores the remaining, like "3rd_level:4th_level:html_file". You will always need to break down when creating reports as the complete page name comes from 2 eVar and you need to balance well how many levels go into the first eVar as there is a limit of 255 characters.
However, the best option is still to review the page name structure to keep it short and within 255.