[itsme]

Lyricist:
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Currently the custom group would be the way to go.
You can rename the custom group, you have a tab like composer, you can choose from a list of existing lyricists instead of having to type it again and again, and (maybe most important) you can maintain a certain entry in one place (in case of typos or to replace abbreviations) instead of having to correct hundreds of custom field entries
"... I will want to use it at another time for something else ..." - you're not the only one, that's why more custom groups, more custom fields and renaming of custom fields have been requested many times
another possibility: use the Composer group for both Composer and Lyricist and add a postfix or prefix that specifies the role
example:
George Gershwin ( c )|Ira Gershwin ( l )
George Gershwin (m)|Ira Gershwin (t)
c: George Gershwin|l: Ira Gershwin
m: George Gershwin|t: Ira Gershwin
with c composer, l lyricist, m music, t text or whatever
The pipe symbol | is the separator to be used if you want to see two entries in the list of composers.
I would prefer the postfix as it sorts also nicely in case the role  is not specified (it's often not mentioned on sheet music who contributed what)


Corrections in MSP and aliases:
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I suppose you make corrections as MSP annotations.
You will need to rework your PDFs to transfer the annotations so that they are available in any alias.
And you will have to do that frequently, otherwise you will get lost sooner or later.

To find corrected songs I use two possibilities:
1.) I have an additional collection TODO (or SourceType) where I add the songs that need corrections
2.) In the thread http://zubersoft.com/mobilesheets/forum/...p?tid=3415
Sciurius posted an SQL statement that searches for files with annotations