i was the one who turned it into a bookmarklet :~P
Code
javascript:void eval("!function(){const e=['!function(){"use strict";function e(e){return e.replace("MorphicPreferences.isFlat","MorphicPreferences.isLight")}function n(n){var t=e(new Function("return "+n)().toString());new Function(n+" = "+t)()}MorphicPreferences.isLight=MorphicPreferences.isFlat,IDE_Morph.prototype.darkDesign=function(){this.setDarkDesign(),this.refreshIDE()},IDE_Morph.prototype.lightDesign=function(){this.setLightDesign(),this.refreshIDE()},n("IDE_Morph.prototype.createLogo"),n("IDE_Morph.prototype.createControlBar"),n("IDE_Morph.prototype.createCategories"),n("IDE_Morph.prototype.createSpriteBar"),n("IDE_Morph.prototype.createCorralBar");var t=e(IDE_Morph.prototype.setDefaultDesign.toString()),r=e(IDE_Morph.prototype.setFlatDesign.toString());const i=new Function("IDE_Morph.prototype.setDarkDesign = "+t),o=new Function("IDE_Morph.prototype.setLightDesign = "+r);i(),o(),IDE_Morph.prototype.setFlatDesign=function(){MorphicPreferences.isFlat=!0,IDE_Morph.prototype.scriptsPaneTexture=null},IDE_Morph.prototype.setDefaultDesign=function(){MorphicPreferences.isFlat=!1,IDE_Morph.prototype.scriptsPaneTexture=this.scriptsTexture()},console.log("Injecting menu items");var s=IDE_Morph.prototype.settingsMenu.toString().split("\\n addPreference(\\n \'Flat design\',\\n () => {\\n if (MorphicPreferences.isFlat) {\\n return this.defaultDesign();\\n }\\n this.flatDesign();\\n },\\n MorphicPreferences.isFlat,\\n \'uncheck for default\\\\nGUI design\',\\n \'check for alternative\\\\nGUI design\',\\n false\\n );");s.splice(1,0," addPreference(\\n \'Flat design\',\\n () => {\\n if (MorphicPreferences.isFlat) { return this.defaultDesign();\\n }\\n this.flatDesign();\\n }, MorphicPreferences.isFlat,\\n \'uncheck for default\\\\nGUI design\', \'check for alternative\\\\nGUI design\',\\n false\\n );\\n\\taddPreference(\\n \'Dark Design\',\\n () => {\\n if (MorphicPreferences.isLight) {\\n return this.darkDesign();\\n }\\n this.lightDesign();\\n },\\n !MorphicPreferences.isLight,\\n \'uncheck for default\\\\nGUI design\',\\n \'check for alternative\\\\nGUI design\',\\n false\\n );");var p=s.join("");new Function("IDE_Morph.prototype.settingsMenu = "+p)()}();'],n=[[,]],t="0.2003274161194426-1662169419886-userscripts-ran",r=e.length;function i(e,n){const[t,r]=e;for(const e of r)if(o(e,n))return!1;for(const e of t)if(o(e,n))return!0;return 0===t.length}function o(e,n){let t;return t=e.startsWith("/")&&e.endsWith("/")?new%20RegExp(e.slice(1,-1)):function(e){let%20n=e;for(let%20e=0;e%3Cs.length;e++){const%20t=s[e],r=c[e];n=n.replace(r,%22\\%22+t)}return%20new%20RegExp(%22^%22+n.replace(/\/g,%22.%22)+%22$%22,%22i%22)}(e),t.test(n)}const%20s=[%22\\%22,%22.%22,%22+%22,%22?%22,%22^%22,%22$%22,%22(%22,%22)%22,%22[%22,%22]%22,%22{%22,%22}%22,%22|%22],c=s.map((e=%3Enew%20RegExp(%22\\%22+e,%22g%22)));!function(){if(!window[t]||confirm(%22Are%20you%20sure%20you%20want%20to%20run%20the%20userscripts%20again?%22)){window[t]=!0,window.isRunningAsBookmarkletUserscript=!0;for(let%20t=0;t%3Cr;t++){const%20r=e[t];if(i(n[t],location.href))try{window.eval(r)}catch(e){console.error(e)}}delete%20window.isRunningAsBookmarkletUserscript}}()}();%22)