In Unity add a menu item that toggles between dynamic and the default profiler sample size.

DynamicProfilerSamplesSize.cs

using UnityEngine;
using UnityEditor;

[InitializeOnLoad]
public static class DebugMenu
{
	private static int defaultMaxNumberOfSamplesPerFrame = -1;
	private static bool dynamicProfilerSamplesSize = false;
	private const string toggleDynamicProfilerSamplesSizeName = "Debug/Dynamic Profiler Sample Size";
	
	static DebugMenu()
	{
		if (defaultMaxNumberOfSamplesPerFrame == -1)
			defaultMaxNumberOfSamplesPerFrame = Profiler.maxNumberOfSamplesPerFrame;
	}
	
	[MenuItem(toggleDynamicProfilerSamplesSizeName)]
	public static void ToggleDynamicProfilerSamplesSize()
	{
		dynamicProfilerSamplesSize = !dynamicProfilerSamplesSize;
		Menu.SetChecked(toggleDynamicProfilerSamplesSizeName, dynamicProfilerSamplesSize);
		Profiler.maxNumberOfSamplesPerFrame = dynamicProfilerSamplesSize ? -1 : defaultMaxNumberOfSamplesPerFrame;
		if (dynamicProfilerSamplesSize)
			Debug.LogWarning("Profiler sample size is set to dynamic");
		else
			Debug.Log("Profiler sample size has been set back to " + defaultMaxNumberOfSamplesPerFrame);
	}
}

Drop this file in a folder called Editor within your Assets folder. You'll find the new item in the menu at Debug -> Dynamic Profiler Sample Size