Editing the registry is something I often did when writing such items as installation packages.

It is possible to save any part of, or even all the registry, to a text file, which by default has the extension, ".reg". You may use these to restore deleted parts of the registry if things have gone wrong. (Backing up the entire registry is a time-consuming process, and results in an enormous .reg file).

Note by the way, that importing a .reg or other file, will restore deleted entries or overwrite changed entries, but not delete entries added since the file was created.

Deleting items in the registry will usually leave widowed and orphaned entries, in the HKEY_LOCAL_MACHINE\Software\Classes\CLSID and/or HKEY_CLASSES_ROOT\Software\Classes\CLSID keys. These may sometimes come back to haunt you if you manually delete entries relating to imperfectly deleted software, which you then reinstall. Manually chasing widows and orphans, and ensuring that they truly have no dependants, is usually a whole morning's work. (As in real life, I suppose...)

(Purely as an experiment, I once wrote myself a scatter-gun application to clear all widows and orphans from the registry. Many applications hide their licensing features in encrypted entries in the registry. Running my blunderbuss, I found that some applications refused to run; no license detected. Good marks to their writers. Others suddenly ran with no end-of-license date, or restriction on number of users etc. Bad marks.)