A translation from the Larcade Volume one:
"Schlossgarde:
Before ending this chapter on the mitres, we need to have a closer look at the mitres for a small unit "zu Fuss", “on Foot”; a unit that was part of the Königliches Haus of the König of Preussen.
Initialy named the "Preussische Garde Unteroffizier Kompanie"; later; in 1861; renamed "Preussische Garde Unteroffizier Schlossgarde Kompanie". This Schlossgarde Kompagnie of the palaces of the Prussian King was composed of 70 non-commissioned officers; all veterans; in the rank of Vize-Feldwebel. This Kompanie was commanded by a Flügel Adjutant des Königs. This unit served as the Guard within the Royal Palaces; along with the Leib-Gendarmerie, they formed the immediate bodyguard for the sovereigns.
1842: according to their duty; they had two particular pieces of headgear:
*a Zweispitz (bicorne) decorated with black plumes.
*a mitre; identical to the Mod 1824, as worn by the Grenadiere of the 1. Garde Regiment zu Fuss, but with all metal fittings silver-plated.
From 1861 until 1918: the Zweispitz will be replaced by a helmet as worn with the Ordonnanz Uniform (Kleine Dienstuniform-Service uniform). This is the Mod 1860 helmet for the Garde Infantry; with all fittings-the flat chinscales included-in silverplated whitemetal.
Unless the fact that the height of the Helmglocke is reduced gradually til the year 1895- the Pickelhaube keeps its squared Vorderschirm/visor; the smooth Helmspitze on + basis and the chinscales.
31 december 1896: the Kompanie receives a new model of mitre. In all points identical to the one that is worn by the Füsilier Bn of the 1. Garde Regt zu Fuss since 9 February 1894. "
Hope this is the info you're looking for.
Rgds,
Francis