Instead of modifying kde-servicemenus-rootactions PKGBUILD, used updated PKGBUILD for dolphin-root.
Edit - provides array instead of replaces array in the updated PKGBUILD.
During installation pacman prompted to resolve conflict so first dolphin was removed and then dolphin-root was installed. Even kde-servicemenus-rootactions did not complain. All good now.
$ sudo pacman -U dolphin-root-17.04.0-1-x86_64.pkg.tar.xz
[sudo] password for mickey:
looking for conflicting packages...
:: dolphin-root and dolphin are in conflict. Remove dolphin? [y/N] y
Packages (2) dolphin-17.04.0-1 [removal] dolphin-root-17.04.0-1
Total Installed Size: 8.21 MiB
Net Upgrade Size: 0.00 MiB
:: Proceed with installation? [Y/n] y